## Restrict Allowed Blocks in Post Type to single Embed

Question

I am trying to limit the allowable blocks in a custom post type to just a YouTube video block. It appears there may have been some changes in 5.6 because this used to work:

/**
* Limit blocks to the following for Video
*
* @param array|bool $allowed_block_types Allowed Block Types. * @param WP_Post$post                Current Post.
*
* @return string[]|bool
*/
function barasch_video_allowed_blocks( $allowed_block_types, WP_Post$post ) {
if ( 'video' !== $post->post_type ) { return$allowed_block_types;
}
}

add_filter( 'allowed_block_types', 'barasch_video_allowed_blocks', 10, 2 );


As it currently stands, you can’t add any blocks because core-embed/youtube appears to no longer be recognized when specified in allowable blocks. If I change core-embed/youtube to core/embed, that allows the blocks to reappear but I see all available embed blocks which I’d like to avoid if possible.

Strangely, when registering the custom post type, the YouTube block does appear as shown below if I specify it within the template, so I’m at a loss as to what is going on. It appears that the core-embed/youtube slug is recognized when declaring the template, but not when specifying allowed blocks.

register_post_type(
'video',
[
.... remaining arguments ....
'template'            => [
[