I have more news. Unfortunately, none of it is good.
First, the 2025-06 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5060842) was installed today. That did not fix my device not showing up in the Microsoft account device page.
Second, I tried a repair install (download the Microsoft windows 11 ISO, mount it, run setup, and keep all). This did not fix the problem either.
The only thing I would have left to try is a clean install, but it sounds like the person who started this thread already did that.
I guess we have to wait a month and bug Microsoft after that. :-(