Outlook Continually Prompting for Password

This worked for me with Outlook 365

Ensuring Modern Authentication on the local PC. Also check Modern Authentication is turned on within the Microsoft 365 tenant.
Open Regedit and navigate to the following locations:

Edit or create the DWORD – “EnableADAL”  Set the value to 1

Create a DWORD – “AlwaysUseMSOAuthForAutoDiscover”  set the value to 1

Other Checks

  • Run ScanPST on the Outlook Data file
  • Run SFC/scannow
  • Run DISM /Online /Cleanup-Image /CheckHealth
  • Run DISM /Online /Cleanup-Image /ScanHealth
  • Run Outlook Updates
  • Download the Microsoft Microsoft Support and Recovery Assistant (SARA) from the following location and check Outlook
  • Rename the Outlook OST file

Uninstall Microsoft Office

As a last resort, you can try uninstalling Microsoft Office and completely deleting remaining folders and reg keys.  And reinstall office again

Navigate to Regedit and Delete the folder office from the file path :

  1.  HKEY_CURRENT_USER\Software\Microsoft\
  3.  C:\Users\(User)\AppData\Roaming\Microsoft\
  4.  C:\Users\(User)\AppData\Local\Microsoft\