Many Mac computers in my company suddenly started to experience intermittent "Grant Access" dialogs upon saving Excel files on desktop. The timing for all of these computers seems more than a coincidence. In conjunction with this timing, some users have various problems saving (causing Excel to freeze and must be force-quit) or re-opening files (Excel file can not be read and opened, and I had to load the files in Google Sheets to retrieve the data, which appeared perfectly intact). If a file is passed to another computer, it opens fine, so it's not a file issue - it's a software issue. All software is updated, and these are locally stored files - they are not on OneDrive, nor are they shared.
We have reset permissions on the Mac per Microsoft's guidance, but that didn't resolve the issue. Our only work-around is uninstalling Excel version 16, and reverting back to Excel version 15, but that is not a long term solution because it means we can't perform software updates.
This has been plaguing us since version 16 was introduced. Some computers encounter it more than others, and if a computer doesn't experience this often, I didn't revert that one back to version 15. However, for the remaining computers who are stuck in version 15, I need to eventually let them start updating again, although the users of those computers won't let me upgrade them until I am 100% confident in the solution. They don't want to be guinea pigs for testing solutions.