我需要的正是您所要求的功能，所以我做了一个自定义端点。它只公开了一个WP_REST_Server::READABLE请求多个职位，但它似乎工作得很好。
大多数特定于post类型的东西都被简单地转发到WP_REST_Posts_Controller示例，这些示例会为每个查询结果示例化。我希望这将降低与其他插件或未来API更新的兼容性问题的风险。
请随意使用下面的代码：

/**
 * Custom endpoint for querying for multiple post-types.
 * Mimics `WP_REST_Posts_Controller` as closely as possible.
 *
 * New filters:
 *  - `rest_multiple_post_type_query` Filters the query arguments as generated
 *    from the request parameters.
 *
 * @author Ruben Vreeken
 */
class WP_REST_MultiplePostType_Controller extends WP_REST_Controller
{

    public function __construct()
    {
        $this->version   = '2';
        $this->namespace = 'websiteje/v' . $this->version;
        $this->rest_base = 'multiple-post-type';
    }

    /**
     * Register the routes for the objects of the controller.
     */
    public function register_routes()
    {
        register_rest_route($this->namespace, '/' . $this->rest_base, array(
            array(
                'methods'             => WP_REST_Server::READABLE,
                'callback'            => array($this, 'get_items'),
                'permission_callback' => array($this, 'get_items_permissions_check'),
                'args'                => $this->get_collection_params(),
            ),
        ));
    }

    /**
     * Check if a given request has access to get items
     *
     * @return bool
     */
    public function get_items_permissions_check($request)
    {
        return true;
    }

    /**
     * Get a collection of items
     *
     * @param WP_REST_Request  $request  Full data about the request.
     * @return WP_Error|WP_REST_Response
     */
    public function get_items($request)
    {
        $args                        = array();
        $args['author__in']          = $request['author'];
        $args['author__not_in']      = $request['author_exclude'];
        $args['menu_order']          = $request['menu_order'];
        $args['offset']              = $request['offset'];
        $args['order']               = $request['order'];
        $args['orderby']             = $request['orderby'];
        $args['paged']               = $request['page'];
        $args['post__in']            = $request['include'];
        $args['post__not_in']        = $request['exclude'];
        $args['posts_per_page']      = $request['per_page'];
        $args['name']                = $request['slug'];
        $args['post_type']           = $request['type'];
        $args['post_parent__in']     = $request['parent'];
        $args['post_parent__not_in'] = $request['parent_exclude'];
        $args['post_status']         = $request['status'];
        $args['s']                   = $request['search'];

        $args['date_query'] = array();
        // Set before into date query. Date query must be specified as an array
        // of an array.
        if (isset($request['before'])) {
            $args['date_query'][0]['before'] = $request['before'];
        }

        // Set after into date query. Date query must be specified as an array
        // of an array.
        if (isset($request['after'])) {
            $args['date_query'][0]['after'] = $request['after'];
        }

        if (is_array($request['filter'])) {
            $args = array_merge($args, $request['filter']);
            unset($args['filter']);
        }

        // Ensure array of post_types
        if (!is_array($args['post_type'])) {
            $args['post_type'] = array($args['post_type']);
        }

        /**
         * Filter the query arguments for a request.
         *
         * Enables adding extra arguments or setting defaults for a post
         * collection request.
         *
         * @see https://developer.wordpress.org/reference/classes/wp_user_query/
         *
         * @param array            $args     Key value array of query var to query value.
         * @param WP_REST_Request  $request  The request used.
         *
         * @var Function
         */
        $args       = apply_filters("rest_multiple_post_type_query", $args, $request);
        $query_args = $this->prepare_items_query($args, $request);

        // Get taxonomies for each of the requested post_types
        $taxonomies = wp_list_filter(get_object_taxonomies($query_args['post_type'], 'objects'), array('show_in_rest' => true));

        // Construct taxonomy query
        foreach ($taxonomies as $taxonomy) {
            $base = !empty($taxonomy->rest_base) ? $taxonomy->rest_base : $taxonomy->name;

            if (!empty($request[$base])) {
                $query_args['tax_query'][] = array(
                    'taxonomy'         => $taxonomy->name,
                    'field'            => 'term_id',
                    'terms'            => $request[$base],
                    'include_children' => false,
                );
            }
        }

        // Execute the query
        $posts_query  = new WP_Query();
        $query_result = $posts_query->query($query_args);

        // Handle query results
        $posts = array();
        foreach ($query_result as $post) {
            // Get PostController for Post Type
            $postsController = new WP_REST_Posts_Controller($post->post_type);

            if (!$postsController->check_read_permission($post)) {
                continue;
            }

            $data    = $postsController->prepare_item_for_response($post, $request);
            $posts[] = $postsController->prepare_response_for_collection($data);
        }

        // Calc total post count
        $page        = (int) $query_args['paged'];
        $total_posts = $posts_query->found_posts;

        // Out-of-bounds, run the query again without LIMIT for total count
        if ($total_posts < 1) {
            unset($query_args['paged']);
            $count_query = new WP_Query();
            $count_query->query($query_args);
            $total_posts = $count_query->found_posts;
        }

        // Calc total page count
        $max_pages = ceil($total_posts / (int) $query_args['posts_per_page']);

        // Construct response
        $response = rest_ensure_response($posts);
        $response->header('X-WP-Total', (int) $total_posts);
        $response->header('X-WP-TotalPages', (int) $max_pages);

        // Construct base url for pagination links
        $request_params = $request->get_query_params();
        if (!empty($request_params['filter'])) {
            // Normalize the pagination params.
            unset($request_params['filter']['posts_per_page']);
            unset($request_params['filter']['paged']);
        }
        $base = add_query_arg($request_params, rest_url(sprintf('/%s/%s', $this->namespace, $this->rest_base)));

        // Create link for previous page, if needed
        if ($page > 1) {
            $prev_page = $page - 1;
            if ($prev_page > $max_pages) {
                $prev_page = $max_pages;
            }
            $prev_link = add_query_arg('page', $prev_page, $base);
            $response->link_header('prev', $prev_link);
        }

        // Create link for next page, if needed
        if ($max_pages > $page) {
            $next_page = $page + 1;
            $next_link = add_query_arg('page', $next_page, $base);
            $response->link_header('next', $next_link);
        }

        return $response;
    }

    /**
     * Determine the allowed query_vars for a get_items() response and prepare
     * for WP_Query.
     *
     * @param  array            $prepared_args
     * @param  WP_REST_Request  $request
     *
     * @return array            $query_args
     */
    protected function prepare_items_query($prepared_args = array(), $request = null)
    {

        $valid_vars = array_flip($this->get_allowed_query_vars($request['type']));
        $query_args = array();
        foreach ($valid_vars as $var => $index) {
            if (isset($prepared_args[$var])) {
                /**
                 * Filter the query_vars used in `get_items` for the constructed
                 * query.
                 *
                 * The dynamic portion of the hook name, $var, refers to the
                 * query_var key.
                 *
                 * @param mixed  $prepared_args[  $var ] The query_var value.
                 */
                $query_args[$var] = apply_filters("rest_query_var-{$var}", $prepared_args[$var]);
            }
        }

        // Only allow sticky psts if 'post' is one of the requested post types.
        if (in_array('post', $query_args['post_type']) || !isset($query_args['ignore_sticky_posts'])) {
            $query_args['ignore_sticky_posts'] = true;
        }

        if ('include' === $query_args['orderby']) {
            $query_args['orderby'] = 'post__in';
        }

        return $query_args;
    }

    /**
     * Get all the WP Query vars that are allowed for the API request.
     *
     * @return array
     */
    protected function get_allowed_query_vars($post_types)
    {
        global $wp;
        $editPosts = true;

        /**
         * Filter the publicly allowed query vars.
         *
         * Allows adjusting of the default query vars that are made public.
         *
         * @param array  Array  of allowed WP_Query query vars.
         *
         * @var Function
         */
        $valid_vars = apply_filters('query_vars', $wp->public_query_vars);

        /**
         * We allow 'private' query vars for authorized users only.
         *
         * It the user has `edit_posts` capabilty for *every* requested post
         * type, we also allow use of private query parameters, which are only
         * undesirable on the frontend, but are safe for use in query strings.
         *
         * To disable anyway, use `add_filter( 'rest_private_query_vars',
         * '__return_empty_array' );`
         *
         * @param array  $private_query_vars  Array of allowed query vars for
         *                                    authorized users.
         *
         * @var boolean
         */
        $edit_posts = true;
        foreach ($post_types as $post_type) {
            $post_type_obj = get_post_type_object($post_type);
            if (!current_user_can($post_type_obj->cap->edit_posts)) {
                $edit_posts = false;
                break;
            }
        }
        if ($edit_posts) {
            $private    = apply_filters('rest_private_query_vars', $wp->private_query_vars);
            $valid_vars = array_merge($valid_vars, $private);
        }

        // Define our own in addition to WP's normal vars.
        $rest_valid = array(
            'author__in',
            'author__not_in',
            'ignore_sticky_posts',
            'menu_order',
            'offset',
            'post__in',
            'post__not_in',
            'post_parent',
            'post_parent__in',
            'post_parent__not_in',
            'posts_per_page',
            'date_query',
        );
        $valid_vars = array_merge($valid_vars, $rest_valid);

        /**
         * Filter allowed query vars for the REST API.
         *
         * This filter allows you to add or remove query vars from the final
         * allowed list for all requests, including unauthenticated ones. To
         * alter the vars for editors only, {@see rest_private_query_vars}.
         *
         * @param array {
         *    Array of allowed WP_Query query vars.
         *
         *    @param string $allowed_query_var The query var to allow.
         * }
         */
        $valid_vars = apply_filters('rest_query_vars', $valid_vars);

        return $valid_vars;
    }

    /**
     * Get the query params for collections of attachments.
     *
     * @return array
     */
    public function get_collection_params()
    {
        $params = parent::get_collection_params();

        $params['context']['default'] = 'view';

        $params['after'] = array(
            'description'       => __('Limit response to resources published after a given ISO8601 compliant date.'),
            'type'              => 'string',
            'format'            => 'date-time',
            'validate_callback' => 'rest_validate_request_arg',
        );

        $params['author'] = array(
            'description'       => __('Limit result set to posts assigned to specific authors.'),
            'type'              => 'array',
            'default'           => array(),
            'sanitize_callback' => 'wp_parse_id_list',
            'validate_callback' => 'rest_validate_request_arg',
        );
        $params['author_exclude'] = array(
            'description'       => __('Ensure result set excludes posts assigned to specific authors.'),
            'type'              => 'array',
            'default'           => array(),
            'sanitize_callback' => 'wp_parse_id_list',
            'validate_callback' => 'rest_validate_request_arg',
        );

        $params['before'] = array(
            'description'       => __('Limit response to resources published before a given ISO8601 compliant date.'),
            'type'              => 'string',
            'format'            => 'date-time',
            'validate_callback' => 'rest_validate_request_arg',
        );
        $params['exclude'] = array(
            'description'       => __('Ensure result set excludes specific ids.'),
            'type'              => 'array',
            'default'           => array(),
            'sanitize_callback' => 'wp_parse_id_list',
        );
        $params['include'] = array(
            'description'       => __('Limit result set to specific ids.'),
            'type'              => 'array',
            'default'           => array(),
            'sanitize_callback' => 'wp_parse_id_list',
        );

        $params['menu_order'] = array(
            'description'       => __('Limit result set to resources with a specific menu_order value.'),
            'type'              => 'integer',
            'sanitize_callback' => 'absint',
            'validate_callback' => 'rest_validate_request_arg',
        );

        $params['offset'] = array(
            'description'       => __('Offset the result set by a specific number of items.'),
            'type'              => 'integer',
            'sanitize_callback' => 'absint',
            'validate_callback' => 'rest_validate_request_arg',
        );
        $params['order'] = array(
            'description'       => __('Order sort attribute ascending or descending.'),
            'type'              => 'string',
            'default'           => 'desc',
            'enum'              => array('asc', 'desc'),
            'validate_callback' => 'rest_validate_request_arg',
        );
        $params['orderby'] = array(
            'description'       => __('Sort collection by object attribute.'),
            'type'              => 'string',
            'default'           => 'date',
            'enum'              => array(
                'date',
                'id',
                'include',
                'title',
                'slug',
            ),
            'validate_callback' => 'rest_validate_request_arg',
        );

        $params['orderby']['enum'][] = 'menu_order';

        $params['parent'] = array(
            'description'       => __('Limit result set to those of particular parent ids.'),
            'type'              => 'array',
            'sanitize_callback' => 'wp_parse_id_list',
            'default'           => array(),
        );
        $params['parent_exclude'] = array(
            'description'       => __('Limit result set to all items except those of a particular parent id.'),
            'type'              => 'array',
            'sanitize_callback' => 'wp_parse_id_list',
            'default'           => array(),
        );

        $params['slug'] = array(
            'description'       => __('Limit result set to posts with a specific slug.'),
            'type'              => 'string',
            'validate_callback' => 'rest_validate_request_arg',
        );
        $params['status'] = array(
            'default'           => 'publish',
            'description'       => __('Limit result set to posts assigned a specific status.'),
            'sanitize_callback' => 'sanitize_key',
            'type'              => 'string',
            'validate_callback' => array($this, 'validate_user_can_query_private_statuses'),
        );
        $params['filter'] = array(
            'description' => __('Use WP Query arguments to modify the response; private query vars require appropriate authorization.'),
        );

        $taxonomies = wp_list_filter(get_object_taxonomies(get_post_types(array(), 'names'), 'objects'), array('show_in_rest' => true));
        foreach ($taxonomies as $taxonomy) {
            $base = !empty($taxonomy->rest_base) ? $taxonomy->rest_base : $taxonomy->name;

            $params[$base] = array(
                'description'       => sprintf(__('Limit result set to all items that have the specified term assigned in the %s taxonomy.'), $base),
                'type'              => 'array',
                'sanitize_callback' => 'wp_parse_id_list',
                'default'           => array(),
            );
        }
        return $params;
    }

    /**
     * Validate whether the user can query private statuses
     *
     * @param  mixed             $value
     * @param  WP_REST_Request   $request
     * @param  string            $parameter
     *
     * @return WP_Error|boolean
     */
    public function validate_user_can_query_private_statuses($value, $request, $parameter)
    {
        if ('publish' === $value) {
            return true;
        }

        foreach ($request["type"] as $post_type) {
            $post_type_obj = get_post_type_object($post_type);
            if (!current_user_can($post_type_obj->cap->edit_posts)) {
                return new WP_Error('rest_forbidden_status', __('Status is forbidden'), array(
                    'status'    => rest_authorization_required_code(),
                    'post_type' => $post_type_obj->name,
                ));
            }
        }

        return true;
    }

}

要注册端点，可以使用类似于以下内容的代码：

add_action('rest_api_init', 'init_wp_rest_multiple_post_type_endpoint');
function init_wp_rest_multiple_post_type_endpoint()
{
    $controller = new WP_REST_MultiplePostType_Controller();
    $controller->register_routes();
}

有人根据Ruben Ray Vreeken的Accepted Answer构建了一个插件：
https://github.com/elevati/wp-api-multiple-posttype
对我来说就像一种魔力。