So post upgrade on this laptop clearly indicates the Intel Graphics Drivers for Windows 8.1 are what was halting the upgrade directly to Windows 10 21H1. I'm curious now if I could have made the jump directly had I know that in advance.
Past upgrades on older versions of Windows 10 had the ability to simply exclude software and drivers that wouldn't work, that functionality has been apparently removed somewhere along the way. Which is only reinforcing the Windows 11 line in the sand reality... MS is shedding support for older hardware, and this is obviously happening live now. Windows 10 21H1's installer is not designed to do Windows 8.1 upgrades anymore.
So for everyone here we're going to have to archive old versions of installation media so we can get machines as current as possible via an easy if time consuming process. Our only other alternative is to maintain our own database of known drivers that cause issues with the process. Which is very likely to be wrong all the time. All this injects time and cost into supporting older gear which is only reinforcing the drive of replace, not upgrade.
At very least pushing all these old rigs into a N&P situation as a fallback. Which solves the problem obviously.
Also on this unit, it's a touch enabled ASUS X550LA laptop. The Asus Smart Gesture software installed by Win10 itself was wrong to enable the touchpad no the unit. The screen worked fine, but the tap pad was toast. Installing the correct version requires the old one to be gone, which requires a reboot, which caused Win10 to reinstall the bad one. Ultimately I had to use Revo to remove the "bad one", which got the registry entries enough such that the proper version would actually install and on next reboot I had working touch devices.
A process that's highly annoying and yet also likely to impact a fresh load. Even MORE reason to shed support of this old 4th gen platform. I already told the client it was only an hour of labor for all this, so I can't recover the time. But if I were to bill for this I'd have to charge at least 3 hours of labor to cover my costs. That's $300, cheaper to buy a refurb that works.