Comment by fuzzfactor

Very interesting.

Some users have been deleting the entire IrisService in the registry, it appears to also be related to the systray icons on the taskbar.

The first link is a couple years old but the second one is from a couple months ago. Apparently triggered now by the latest update kb5094126, so there may be some questionable new changes going on in this particular monkey-business department:

https://gist.github.com/JMMBA/d56923502a74b6b7196dd800fad0a8...

https://thegeekpage.com/taskbar-missing-after-sign-in-6-fixe...

"Fix 3" is the one where the IrisService reg key is nuked.