Does that mean that you don't (ever) have to login to Microsoft / Office365 online services with the desktop software? I have been hearing that people are having issues with desktop apps asking them to log back in to use them - and they can't.
You don't have to log in anywhere. MS sells Office 365 and Office 2019, 365 being a subscription service and 2019 a one-time purchase. People you talk about probably had issues with desktop apps that were a part of O365.