Cannot login initially Outlook 365 on Mac

Close Outlook 365.
Go to folder

• ~/Library/Group Containers

Erase directories:

• UBF8T346G9.ms
• UBF8T346G9.Office
• UBF8T346G9.OfficeOsfWebHost

Empty the trash bin.
Start Outlook 365.
Make sure when you are using MFA, you are using MS Authenticator for confirmation, not SMS code. If you use SMS code to confirm MFA, you'll end up with the same problem.