Sidebar: Layout shift causes menu items to move for editors

[mmtr]

Issue reported during walkthrough: p58i-iKo-p2

There is a layout shift when a non-admin accesses Calypso for the first time on a new browser which causes the sidebar menu items to suddenly change. This is confusing for folks who click fast enough while the menu is still loading.

For instance, in the video below, the user (who is an editor), wants to click the "Posts" menu and places the mouse cursor over it. Just before clicking it, "Upgrades" and "My Mailboxes" dissappear, so "Posts" is moved two positions to the top, and the cursor is now over "Pages" which is what the user ends up clicking inadvertently.

https://github.com/user-attachments/assets/3342d375-4269-46e3-af6a-e4a3b0ef3a3a

[github-actions[bot]]

OpenAI suggested the following labels for this issue:

• [Feature Group] Editor Experience: The issue relates to the user experience for editors in Calypso, particularly in the sidebar navigation.
• [Feature] Calypso & wp-admin Navigation: The problem described involves navigation within Calypso, where sidebar menu items shift during loading.
• [Feature] User Management: The layout shift affects users with different roles, mainly editors, when accessing the system.