Dear RennieSchmid
We received a response from a user who was able to get back to normal after rolling back Office to version 16.0.17328.20142. We are currently testing this method, but we have received feedback from a user that it resolved the issue, so we suggest you try it.
- Close all Office software, search for "Command Prompt" (or "cmd") in the "Start Menu", and right-click the mouse and select "Run as administrator";
- In the command prompt enter the following code: cd %programfiles% \Common Files\microsoft shared\ClickToRun, and then press Enter;
- And then enter: Officec2rclient.exe /update user updatetoversion=16.0.17328.20142
17328.20142 is the internal version number of the version you want to install, you can also choose an earlier version. Please refer to this link for the specific version number:

Update history for Microsoft 365 Apps (listed by date) - Office release notes | Microsoft Learn (In English)
We hope you find the above information helpful. Whether or not it works, please let us know by replying. Thank you for your understanding.
Best Regards,
Tracy | Microsoft Community Support Specialist
It appears this method works, but only temporarily — the "restart required" message re-appears, often within a matter of hours, and definitely after the next time the computer is restarted.
Is there any hope at all that MS will provide a fix for this, which seems to be a consequence of the most recent Win 11 update?