Description

Currently block patterns show up within the Pattern Library UI, regardless of if the pattern is insertable. Sure, one could add a broken pattern to a page, but its obviously a subpar experience when the "Your site doesn't support.." message shows up.

I suggest that patterns with unregistered blocks are simply omitted from the Pattern Library, so that the experience of adding broken patterns to a site just doesn't occur.

This will become an even bigger deal when the WP Patterns Directory lands - if third party blocks are allowed to be used within partners (as they should).

Step-by-step reproduction instructions

1. Install a block/block plugin, such as CoBlocks
2. Create a pattern to your site using a block from it (I used the coblocks/gallery-carousel block in my example screenshot below).
3. Deactivate the plugin (therefore unregistering the carousel block within the pattern).
4. Open the Pattern Library
5. See the broken pattern

Expected behaviour

Unsupported patterns (patterns that would be broken if added to a page due to unregistered blocks) should not be available to insert via the Pattern Library.

Actual behaviour

I can see and add broken patterns to my site.

Screenshots

WordPress information

• WordPress version: 5.7.1
• Gutenberg version: Not installed
• Are all plugins except Gutenberg deactivated? Yes (except for installing CoBlocks to make a pattern)
• Are you using a default theme (e.g. Twenty Twenty-One)? Yes