A customer's #Windows10 PC logged them in to a generic desktop, with all icons gone except for all-users icons, & unable to open the Start Menu or the notifications fly-out.
I talked them through Quick Assist, which needed an update, but the Microsoft Store button said they needed to install an app to open such links.
They opened CMD, & their home directory was "C:\Users\TEMP". Fun.
The fix:
TenForums, "Fix You've been signed in with a temporary profile in Windows 10": https://www.tenforums.com/tutorials/48012-fix-youve-been-signed-temporary-profile-windows-10-a.html
I should be even more worried about the number of breakages that need registry dives to fix.
Windows needs the registry to do most things. Registry changes are committed instantly. There's no undo in the registry. If you change or delete any of the wrong keys or values, you could make your PC unbootable. Registry dives are *NOT* to be done lightly.