DOC示例：

#[Route('/blog/{date}/{slug}/comments/{comment_slug}')]
#[ParamConverter('post', options: ['mapping' => ['date' => 'date', 'slug' => 'slug']])]
#[ParamConverter('comment', options: ['mapping' => ['comment_slug' => 'slug']])]
public function showComment(Post $post, Comment $comment)
{
}

"所以，在你的情况下，你必须有："

#[Route('/{slug}/{subSlug}', name: 'subcategory')]
#[ParamConverter('cat', options: ['mapping' => ['slug' => 'slug']])]
#[ParamConverter('sub', options: ['mapping' => ['subSlug' => 'slug']])]
public function (Category $cat, Subcategory $sub): Response
{
}

方法中的参数名必须与paramConverter中的参数名相同，
文件：
https://symfony.com/bundles/SensioFrameworkExtraBundle/current/annotations/converters.html
apply（）方法在配置被支持时被调用，根据请求属性，它应该设置一个名为$configuration-〉getName（）的属性，该属性存储一个类为$configuration-〉getClass（）的对象。
按照您的代码，对象在$request-〉属性上设置为 * category！= $cat（您的参数），subCategory！= $sub，您将使用null而不是对象

名称必须相同

#[Route('/{slug}/{subSlug}', name: 'subcategory')]
#[Entity('category', expr: 'repository.findOneBySlug(slug)')]
#[Entity('subcategory', expr: 'repository.findOneBySlug(subSlug)')]
public function subcat(Category $category, Subcategory $subcategory): Response