I also got this issue, and Microsoft Support helped me, and the problem solved.
the following steps fixed the issue.
1- Ensure Outlook and Windows are fully updated.
2-Clear the Stale Credentials under Windows Credential in the Credential manager.
3- Delete the Outlook profile.
4- Delete everything under this location: C:\Users\(User)\AppData\Roaming\Microsoft\OutlookNote: you can get to AppData by placing %AppData% in the address bar for Windows Explorer and pressing “Enter”, it will default to “Roaming”.
5: Delete everything under this location: C:\Users\(User)\AppData\Local\Microsoft\Outlook
6:Flush the DNS cache in the computer by running the command prompt as an admin (bottom left, type CMD and right click on the result for command promt, and chose, run as an administrator), and typing the command: IPConfig /flushdns
7: Reboot the computer.
8: Connect the account back in a new profile and test.