Using Classic Outlook on Windows for personal email, calendar, and contact management
I can't see this behaviour..
FYI
Microsoft 365 Roadmap | Microsoft 365
Shared Mailboxes can be added as Accounts in the new Outlook for Windows. The Shared Mailbox will appear at the Account Level in the Folder list. Access to the Shared Mailbox requires the user's credentials and associated permissions.
Rollout Start: July 2024