Using older versions of Outlook for Mac in business environments
FYI - reply from Microsoft support after trying to troubleshoot:
We created a report for this, and submitted them to our engineers. I added your ticket to our list for further investigation. A fix has been rolled out the latest Beta version, and you may opt in to the Beta version to get access to the fix earlier, or you may wait for the fix to become available in the current version.
For now, a workaround is to restart your device and it should temporarily fix the issue.
We thank you for your understanding, and patience as we work on this matter thoroughly.