Unchanged meetings always prompt to save changes in Outlook 2016
Possible solution that worked for me: disable "show weather on the calendar" under File->Options->Calendar
Try to open Outlook in safe mode : Outlook.exe /safe.
If this no longer happens, then the problem is with some installed add-on. Try in this case to disable add-ons until you find the problematic one.
I believe the issue is that when you click on a link (e.g. to open a Zoom or Webex link) you have clicked into the body of the meeting causing the application goes into Edit mode. Once it's been in edit mode, it cannot be closed until you save or discard changes.