I tried connecting my outlook.com mail account (
username@live.com) to the MS Outlook desktop app. I have Microsoft 365.
I ran into a problem, apparently with ASR rules.
By default, Outlook desktop uses the Microsoft exchange protocol to sync with outlook.com accounts. I tried to do it that way, and although the initial setup worked, it required restarting the Outlook desktop app, at which point Outlook complained that it could not retrieve the necessary information, and failed to sync. Upon a second restart, it failed to start. This was reproducible.
I then tried setting the account up manually, with the IMAP protocol. This worked, but if you do it this way, you only get your mail synced, but your online Microsoft calendar will not sync.
I then tried the default Microsoft exchange way, but with ASR rules off, and Microsoft Defender at default settings. It worked.
Then I reenabled ASR rules and other high settings for Defender, and Microsoft exchange continues to sync correctly.