When a user gets an error on a Mac in MS Office such as "This file cannot be edited on a Mac," running the license removal tool will allow the user to authenticate their copy of Office once more and license the product correctly. We see this error from time to time when product updates cause license errors specific to macOS.
https://support.office.com/en-gb/article/how-to-remove-office-license-files-on-a-mac-b032c0f6-a431-4dad-83a9-6b727c03b193
https://support.office.com/en-gb/article/troubleshoot-office-for-mac-issues-by-completely-uninstalling-before-you-reinstall-ec3aa66e-6a76-451f-9d35-cba2e14e94c0