Did you ever figure it out,
the same thing happened to me.
Same issue here. Bought Windows 11 Pro lisence, so no upgrading or anything. Installed on a newly built rig with all custom parts. Worked fine for a year or so, and now suddenly not activated. Troubleshooter is completely useless. Doesn't accept the key i have. What is going on here!?
Edit: Also activate now by "using a phone" is not even a option for me, there is no such option. I'm using the version 23H2, build (22635.2486). None of the "steps to get it working" are working. I can't even contact anyone from support, because all support steps lead to the "activate by phone" option, that doesn't exist. Fantastic.
Edit: The only thing i can think of is i used Armoury Crate Uninstall Tool (ASUS) to remove any bloatware/spyware from ASUS running on my system. The issue raised it's ugly head some time after.