Sometimes Microsoft pushes an automatic update that breaks Outlook. We post the eventual fixes here.
May 11, 2021
After automatic update, Outlook is only showing partial messages. The fix is to roll back the update. Open a cmd prompt with admin permissions and run:
“C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe” /update user updatetoversion=16.0.13901.20462
Then pause updates for 7 days in Windows. They should have a fix pushed before then.