Using older versions of Outlook for Mac in business environments
Unfortunately the newest general release version has not fixed this issue (although I haven't gone down the beta release path yet).
I just bought a new MacBook Pro with M1 Pro chip, Monterey, and I'm having the same exact problem.
It's a shame, since I absolutely love both the new laptop and Outlook with iOS and Windows 11 until this "MAC is not syncing sent folder for IMAP account" issue.
I hope Microsoft and Apple resolve this soon.