Using Classic Outlook on Windows for personal email, calendar, and contact management
I have a love-hate relationship with Microsoft, while I hate them for their arrogance in assuming that only they know what is best for the user in this case I cannot agree with your assertion that "Outlook365 is ancient, and hasn't had any significant UI improvement in years". I have been using Oulook for nearly 30 years, while admittedly the basic UI has not changed much (maybe becuase it "just works"), but it has always been evolving and there have indeed been many changes and additions (including to the UI); some of them I like and use, others I don't use and disable. Until recent years when the the marketing dept began to take precedence over developers, many of the changes were in response to user feedback.
Nevertheless, the ever-changing ribbon really makes me angry because there is no way to disable it, somebody in marketing obviously clicked on the "Ignore User Feedback" box.