I just got this from the support guy I have been working with:
- Issue possibly related to latest Office release Version 2406 (Build 17726.20126)
- Based on screenshot, Office client is already in the latest build, no update required. (Error on error - should have been retuning or giving that your Office is already up to date)
- We suggest downloading the previous version and turn OFF automatic updates until the next Office release.
- Reference - Update history for Microsoft 365 Apps (listed by date) - Office release notes | Microsoft Learn
I think I'm just going to leave it on the latest version as there is no indication that the security updates have been compromised and Office is otherwise working fine. When the other machines update, if this one doesn't, I will do an Online Repair and see what happens.
The latest updates are now available. Two of my machines updated, the problematic one returned the error. I performed the Online Update and it looks like that worked, but the error on hitting Update Now still remains. I note that my version is different from the one Pedro posted. Mine is 2406 Build 16.0.17726.20078 on all three machines now.
Ergo, the problem is not resolved with the latest version.