I’ve only ever used Outlook when forced to by an employer and I find it a dreadful application to use. I would guess that most people prefer something else. I would imagine that most people tend to stick with the default email app on their computer (no idea what that is on Windows as I’ve managed to avoid having to use Windows for 7 years now).

They've really shifted how Outlook works... as well as how the backend is more tuned to the way M365 mail works far more than how it used to work with Exchange, or independently. It's been a slow downslide imo since around 2007 or so.

I know the why, but it's really worse as an experience for most people than the older integrations... but the use of horizontally scalable backends makes for a saner platform at the expense of better UX.

Will be removed from the next release. Then you can’t connect to your own exchange server anymore and are forced into 365 when you want a desktop app.