I am one of the users on a multi-user version of Office365. I am a Mac user since 1991. This just started happening about 2-3 weeks ago and every time, I click "Not Now" out of frustration because there's no "Never" response. Every time I restart the machine, the prompt pops up again and I'm getting really pissed off that there is no way to respond "Don't show this prompt again." In the past, I've had updates that have problems and I want to choose which updates I install. I've searched various preferences, indicated that I wanted only manual updates wherever I can find it. I don't see the Microsoft Auto-Update app like was present before Office365. I KNEW Office365 would be something I regret. Is this harassment something that MS thinks is going to win friends and influence people?
Copy-paste from answers.microsoft.com.
The nagging is sent by Notifications in the macOS and can be turned off in System Preferences-->Notifications as mentioned above.
This has no effect at all on when and how Microsoft AutoUpdate works. I just ran MAU to test this. You can still choose "Automatically Check," which will ONLY check (not download and install) and then will alert you if there are updates.
Disabling MAU in Notification Center has no effect on this. I disabled it and the nagging is no longer there. MAU provides its own pop-up notification WITHOUT triggering macOS notification.