Shared mailbox cannot be pinned to Favorite

If you are unable to add a shared mailbox to your Outlook Favorites, you can try the following:
1. Check permission: Make sure you have “Full Access” permission.
2. Right-click: Right-click on the shared mailbox in the folder pane to see if there is a “Show in Favorites” option; if there is no such option, it may be a permission or setting issue.
3. Update Outlook and clear cache: Make sure you are using a version of Outlook that supports this feature and check if it is the latest version.
Clear cache: Close Outlook and delete the contents of the %localappdata%\Microsoft\Outlook\RoamCache folder (only affects the local cache).
4. Re-add shared mailboxes: Try removing and re-adding shared mailboxes.
5. Use Outlook Web (OWA): If you are having problems with the desktop client, try operating through the web version of Outlook.