Description

When I use hybrid theme in WordPress 6.2 beta1 nightly, wide and full width settings are lost from the toolbar.

Also, the wide/full-width cover block becomes the content width.

Step-by-step reproduction instructions

Tested with WordPress 6.2 beta1 nightly without Gutenberg plugin.

1. Use a classic theme without theme.json. I use TT1 (Twenty Twenty-one).
2. Add blocks to the post and set its width to wide or full.
3. Add TT3's theme.json to TT1 theme folder. TT1 is now a hybrid theme.
4. Open the post editor again, wide and full width settings are lost from the toolbar.

Screenshots, screen recording, code snippet

-	TT1 without theme.json	TT1 with theme.json
Cover
Image

Environment info

WP6.2-beta1-55293 (latest nightly via Beta Tester plugin), instawp install
TT1 and theme.json of TT3 included in nightly.
Tested without Gutenberg plugin

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes