OPTION 1 - Disconnect the Work or School account in Windows Settings. To do this, use the following method. First close down Outlook. Hold the Windows + I keys simultaneously to open the Settings window. Then click Accounts > Access work or school to open the accounts settings options.
Now highlight the account you're having issues with and click Disconnect. Once done, open Outlook and you should now be prompted for your username and password.
OPTION 2 - Disable Modern Authentication by regedit to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity, create a DWORD item named EnableADAL and set it to zero.
OPTION 3 - Under the same registry key, create a DWORD item named DisableADALatopWAMOverride and set it to 1.
NOTE: If you try Option 2 or 3 and it doesn't fix it, be sure to delete the key you created. Just to keep things clean and not cause problems later on.