Cannot add submenu items in left navigation pattern

[knice]

Description

There is no way to see or toggle open the UI for adding a submenu item when you build a menu in the left navigation pattern

Step-by-step reproduction instructions

1. Add the left navigation block to a new page
2. Create or add an existing menu
3. Click the button to add a submenu
4. The submenu UI for adding submenu links does not appear

Screenshots, screen recording, code snippet

Environment info

https://wordpress-dev.ucsc.edu

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

Yes

[knice]

Now I'm wondering if we should train users to use the navigation block's settings menu to manage the links and submenu links? Seems like it will be easier to manage the menu there anyway.

[knice]

Closing this.