I noticed stock mail app in latest e/os 2.6 is the same old 6.711 ver which does not support OAuth2 with Hotmail/Outlook.
There’s a new mail app available apparently released 23 hours ago.
I tried to update it while on e/os 2.5 and it errors with “invalid package”. The same occurs now on 2.6
invalid_request: The provided value for the input parameter ‘redirect_uri’ is not valid. The expected value is a URI which matches a redirect URI registered for this client application