Classic Theme: Design => Widgets - when using "Top Toolbar" part of userinterface disappears

[burnuser]

Description

When using "Top toolbar" in Classic Theme => Widgets screen, parts of the userinterface are not visible, depending on "Show / Hide block tools"
Show: Undo, Redo and List View are gone

Having Gutenberg 16.6.0 installed:
also Update, Settings and Options are gone

Step-by-step reproduction instructions

1. Use Classic Theme like Twenty Sixteen or GeneratePress
2. Got to Design => Widgets
3. Activate "top toolbar"
4. Select a block
5. Try to activate List View ...

Screenshots, screen recording, code snippet

WP 6.3.1:

Gutenberg 16.6.0:

Environment info

WP 6.3.1; without and with Gutenberg 16:6.0; Theme: Twenty Sixteen, GeneratePress

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

[t-hamano]

Thanks for the report.

This issue is fixed in #54372 #54329 and will be part of Gutenberg 16.7. Please check to see if this issue is resolved when Gutenberg 16.7 is released as a plugin.