The reboot seems to happen in the early morning (after midnight and before 7 AM) after my not having used it for 5+ hours. System logs show things like “the previous reboot was unexpected”, DistributedDCOM errors, etc., but there is no clear cause that I can determine. Googling suggested running an “in place upgrade” to fix any possibly corrupt files. Is this process REALLY safe and does it REALLY preserve any user data and applications? See Redirecting
In my Windows experience (which ended 15 years ago) the Microsoft forums were hardly a den of computer wing nuts. The reference you provide is November 2021. Lost of people had the same concerns you express. I did not see any reason in the few replies to the OP not to believe the suggest answer.
What kind of quality assurance do you want?
There is one other approach - one that you can completely control. Copy all your data to an external drive. Revert your machine to it factory new condition, upgrade Windows to the current version of Windows 11, download and install all 3rd party software and finally return your data files.
Of course, there is always the backup, fresh install, restore option. I’d backup at least all my data first regardless. Was just looking for someone here who had actually done it and could vouch for its non-destructive nature.