A collection of various known Outlook fixes for login problems :
Run Credential Manager, and if your account is listed ensure that it's correct.
If not correct, fix it.
If correct, try deleting it, reboot and log into Outlook.
Logging-in into Web Outlook might sometimes show an existing problem such as
the need to change the password.
Start Outlook in safe mode by running Outlook.exe /safe and enter the ids if asked.
Unlink the Microsoft Account from Outlook
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.
Under the same registry key, create a DWORD item named DisableADALatopWAMOverride
and set it to 1. See
Microsoft article.
Undo fixes which didn't help.
You might also create a system restore point before starting.
