Using Classic Outlook on Windows for personal email, calendar, and contact management
I have found a solution to this issue here--> https://support.microsoft.com/en-us/office/use-favorites-in-outlook-8913f2d0-b167-48cc-8983-86fa9b0d945f I can verify that this works and allows you to add a shared mailbox to your favorites list, It will not show as <sharedmailbox> inbox. I was able to add 4 shared mailboxes with this process
Hope this helps