Action - Default Post Types

This is used for setting the default post types displayed in the admin panel when admins are setting post type when writing new posts.

Example:

// Add 'memes' as a post type displayed (even if there are none) to admins
add_filter( 'default-post-types', function( $post_types ) {
$post_types[] = 'memes';
return $post_types;
});