你的代码中有一些错误和不必要的东西。请使用以下选项：

// save selected weights as custom cart item data
add_filter( 'woocommerce_add_cart_item_data', 'save_font_weights' );
function save_font_weights( $cart_item_data ) {
    if( isset($_POST['font_weights']) && !empty($_POST['font_weights']) ) {
        $cart_item_data['font_weights'] = wc_clean($_POST['font_weights']);
        $cart_item_data['unique_key'] = md5( microtime().rand() );
    }
    return $cart_item_data;
}
// Display custom cart item data in mini cart, Cart and Checkout pages
add_filter( 'woocommerce_get_item_data', 'output_font_weights', 10, 2 );
function output_font_weights( $cart_data, $cart_item ) {
    if( isset($cart_item['font_weights']) ) {
        $cart_data[] = array(
            'key'   => __('Selected weights', 'woocommerce'),
            'value' => $cart_item['font_weights']
        );
    }
    return $cart_data;
}
// save cart item custom data as order item metadata and display it everywhere on orders and email notifications.
add_action( 'woocommerce_checkout_create_order_line_item', 'save_weights_to_order_item', 10, 4 );
function save_weights_to_order_item( $item, $cart_item_key, $values, $order ) {
    if( isset($values['font_weights']) ) {
        $item->update_meta_data( 'Selected weights', $values['font_weights']);
    }
}

下面我使用2个新的功能，除了现有的代码：

• 我将所选的字体权重按产品添加为订单元数据 （假设这是一个逗号分隔的权重字符串）。在保存之前，我将这个逗号分隔的字符串转换为选定权重的数组。
• 我过滤显示的下载（您需要找出正确的下载值与选定的权重进行比较，以仅保留选定的字体权重。因此，您将用正确的变量替换$some_variable_to_replace，以便与所选权重数组进行比较

注意：在最后一个函数中，我首先列出了您可以从每个下载项目中获取的所有数据，并将其放入您可以使用的变量中。
附加功能：

// save cart item custom data by product as order metadata
add_action( 'woocommerce_checkout_create_order', 'save_weights_to_order' );
function save_weights_to_order( $order ) {
    $weights_by_product = array(); // Initializing
    // Loop through cart items
    foreach( WC()->cart->get_cart() as $item ) {
        if( isset($item['font_weights']) ) {
            $font_weights = str_replace(', ', ',', $item['font_weights']); // removing white spaces
            $font_weights = explode(',', $font_weights); // converting to an array
            $weights_by_product[$item['data']->get_id()] = $font_weights;
        }
    }
    if( !empty($weights_by_product) ) {
        // save weights as order metadata
        $order->update_meta_data( '_selected_weights', $weights_by_product);
    }
}
// filter downloadable items
add_filter( 'woocommerce_order_get_downloadable_items', 'filter_order_downloadable_items', 10, 2 );
function filter_order_downloadable_items( $downloads, $order ) {
    foreach ( $downloads as $key => $download ) {
        // All available data in the $download variable
        $download_url        = $download['download_url'];
        $file_name           = $download['file']['name'];
        $file                = $download['file']['file'];
        $download_id         = $download['download_id'];
        $product_id          = $download['product_id'];
        $product_name        = $download['product_name'];
        $product_url         = $download['product_url'];
        $download_name       = $download['download_name'];
        $order_id            = $download['order_id'];
        $order_key           = $download['order_key'];
        $downloads_remaining = $download['downloads_remaining'];
        $access_expires      = $download['access_expires'];
        // Get all selected weights by product
        if ( $weights_by_product = $order->get_meta('_selected_weights') ) {
            // Get the selected weights for the product ID
            $selected_weights = (array) $weights_by_product[$product_id];
            // Here below, REPLACE $some_variable_to_replace with the correct variable
            if ( ! in_array( $some_variable_to_replace, $selected_weights ) ) {
                unset($downloads[$key]); // Remove the font weight if not selected
            }
        }
    }
    return $downloads;
}

代码放在子主题的functions.php文件中（或插件中）。应该可以的