Site Editor: Navigation sidebar is empty when the menu uses a Page List block #85294

Description

In the Site Editor, Navigation shows an empty sidebar when the menu only has a Page List block, like Twenty Twenty-Five's default menu. The canvas shows the pages, but the sidebar only shows the menu description.

With Gutenberg 24.2.0 the sidebar lists the pages. It's empty with Gutenberg trunk (24.3.0-rc.1) and with WordPress 7.2 Beta 1 without the plugin, so it looks like a regression after 24.2.0. Maybe related to #84005, but I haven't checked.

Step-by-step reproduction instructions

1. On a site with WordPress 7.2 Beta 1 and Twenty Twenty-Five, go to Appearance > Editor > Navigation. In Playground: https://playground.wordpress.net/?wp=beta&theme=twentytwentyfive&url=%2Fwp-admin%2Fsite-editor.php%3Fp%3D%2Fnavigation
2. Open the menu if it isn't open already.
3. The sidebar doesn't list any items, while the canvas shows "Sample Page".

Same result on WordPress 7.1 with Gutenberg trunk: https://playground.wordpress.net/?wp=7.1&gutenberg-branch=trunk&theme=twentytwentyfive&url=%2Fwp-admin%2Fsite-editor.php%3Fp%3D%2Fnavigation

Screenshots, screen recording, code snippet

WordPress 7.2 Beta 1, the sidebar is empty:

Gutenberg 24.2.0 on WordPress 7.1.3, the sidebar lists the page:

Environment info

• WordPress 7.2 Beta 1 without Gutenberg, and WordPress 7.1.3 with Gutenberg trunk (24.3.0-rc.1). Works with Gutenberg 24.2.0.
• Twenty Twenty-Five
• Chromium on macOS (WordPress Playground)

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