OK, but as I've said above, it only happens when I am looking at the Start11 menu after pressing the Windows button on the keyboard. It didn't happen before I installed Start11. It seems reasonable to make a connection. I've uninstalled Start11 so if it happens again with the normal Windows 11 menu I'll be back here to eat my words. Until then..
It's happened again and this time I did lose work. Even every four months is too often. I was looking at a frozen/hung Start11 menu with none of the controls functioning, no keys, no mouse, nothing. So your suggestion above could not be tried. That's the end for Start11 with me.
I certainly can't reproduce the issue freely, it only happens occasionally. But always after pressing the Windows key with me looking at the Start11 menu. If it happens again, I'll try uninstalling Start11; that's a nuisance but not as much as losing work.
It's OS Build 26100.3775.
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