Using older versions of Outlook for Mac for personal email and calendar
Come to think of it, I have a new M1 Mac as well. Most of the people in my office have older laptops, which explains why they aren't having these issues.
I tried reverting to Legacy Outlook temporarily for an hour, switching it back, and the bug cleared up, but then it came back out of nowhere last night (I had not restarted). I did the disable/reenable the Task Pane thing, and the bug went away for now... I hope MS does a fix soon.