Windows 11 installation recurring nightmare!  

Sound good, I'll give it a shot.

Thanks to everyone who helped on this issue, I'll go ahead and mark this as complete.

Maybe Windows Update tried to update some drivers at first restart or other stuff and fails. I would try downloading the Windows 11 ISO, disconnect from the internet (to prevent Windows Update messing with drivers) and then run Setup to upgrade to Windows 11. If your computer is compliant you should see the "Choose what to keep" screen. If it isn't you must bypass compatibility check (see relevant threads on Windows 11 Forum) As a further attempt to eliminate conflicts, you can go in BIOS or Device Manager and disable any non-essential devices, such as sound, LAN, etc. You can also disconnect any external devices such as printers, external hard disks etc. I would also disconnect all disks except the Windows disk. Also disable any third-party antivirus or antimalware just in case it interferes with the upgrade (it might think a virus is replacing system files and block it). Also disable all startup applications and non-Microsoft services until the upgrade is complete.