Description

When editing a theme template, if you add a Group block or a Row block inside a Group block (ie a nested Group or Row) it's not possible to add blocks to the nested Group or Row.

Step-by-step reproduction instructions

1. Edit a block theme template (tested in both tt2 and a newly created block theme)
2. Add a Group block
3. Add a nested Group block inside the parent Group block
4. The UI to add additional blocks inside the nested Group block does not appear.
5. If you switch the nested Group to a nested Row, you also cannot add blocks

Screenshots, screen recording, code snippet

Nested group

Nested row

Environment info

• WordPress 6.0.2 and Gutenberg trunk
• Tested in Brave browser
• Tested on both an M1 Macbook Pro, and Ubuntu 22.04

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