Hello Chemin (and the many others who are plagued with this issue).
This issue is constant (every 10 minutes), and intrusive (because it interrupts what you are presently working on, and demands a response before you can continue with your work).
I tried the recommended "fix", that was provided to you by Microsoft, with the result that each one of my MS Office applications crashed (and continued to do so, after repeated re-starts). This necessitated the removal of all MS Office applications, and then downloading and reinstalling 'fresh versions'.
Of course, I now have working MS Office apps, but also the return of the constant office365service.app gemlin. Surely, someone - either Microsoft or Apple - must have an easy solution to this issue. If they don't, then this doesn't say much about their attitude towards we poor suffering customers.
The bottom line: Why are we expected to have something blatantly and obstinately forced upon us, when we have never asked for it, do not want it, and are not subscribed to a service such as this?
Come on Apple and Microsoft, we do at least deserve an answer and, at least a solution.