Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Did you try a new profile? It sounds like the profile might be corrupt.
You can look at the profile in the registry - check each subkey under this key (assuming the profile is called Outlook) Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\Outlook\9375CFF0413111d3B88A00104B2A6676
Is the gmail address in any of the subkeys? If so, you can try deleting the subkey it is in - and try adding the account again. Or just make a new profile.