Here is what solved it for me. (Copied from: ).
Quit all Office applications (Word, Teams, Outlook, etc). Go to KeyChain Access. Search 'Exchange' under Login - All Items and delete everything.
![Outlook 365 For Mac Login Outlook 365 For Mac Login](/uploads/1/2/5/6/125656605/577735461.jpg)
Unmistakably Office, designed for Mac. Get started quickly with new, modern versions of Word, Excel, PowerPoint, Outlook and OneNote—combining the familiarity of Office and the unique Mac features you love. Office 365 customers get the new Office for Mac first. The recommended application for using the Office 365 service is Outlook. See instructions. These instructions have been prepared for Mac OS X 10.11 (OS X El. As [email protected]); Password: your password; Tap Sign In.
Search 'Office' and delete everything. Search 'ADAL' and delete everything.
Launch Outlook. You will get the activation prompt and then If account is already added you will see the password prompt for app and ADAL again.
![365 365](/uploads/1/2/5/6/125656605/456914108.jpg)
Please do 2-Factor Authentication if asked to. If that doesn't work, do steps 2-4 but restart the Mac before launching Outlook.