https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-outlook-issue-blocking-access-to-emails-calendars/

Microsoft has addressed a known issue affecting Outlook for Microsoft 365 customers that prevented them from accessing group mailboxes and calendars using the Outlook desktop client.

The buggy Outlook version was released to the Current Channel on March 28, and the fix is rolling out to all impacted users with Outlook Desktop Version 2304 Build 16327.20214.