Description

We have a 'hybrid' theme, that uses theme.json and the block editor, but isn't a block theme. When testing out the Command Palette everywhere, I saw "Open Custom CSS" in it. Clicking on it takes me to the site editor and there's an error immediately: "You attempted to edit an item that doesn't exist. Perhaps it was deleted?"

As far as I can tell, there's no other way to get to this screen with menus - only the command palette.

If I save some custom CSS, leave the page and return, I still get the error about editing an item that doesn't exist.

Step-by-step reproduction instructions

1. Use a site with a hybrid theme (theme.json but not a block theme)
2. Open the command palette and click "Open Custom CSS"

Screenshots, screen recording, code snippet

No response

Environment info

• WordPress 6.9-RC2, no 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

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure