The language most likely was changed? What win 10 SKU are you trying to upgrade, using what ISO? Oh wait, heavily crip... ehh... modified install....
It's not voodoo magic. Just use an ISO in the same language as the OS installed (or fix HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\Language to match it.) <--reboot required Eventually set HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\EditionID to EnterpriseS and HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductName to Windows 10 Enterprise LTSC 2021 (no reboot required) then proceed to the in place upgrade.
That's what I'm getting at though, I've confirmed this and the error persists. I'm upgrading from a US eng W7 Install with SP1 and the required updates/patches to a US Eng multi-edition ISO for 10. Still unable to keep programs. Is the problem maybe trying to use the multi-edition ISO?
That is a regular ISO, all Win 10/11 ISOs from 1709 are full AiO (EDIT: not the LTSC ISOs though). What build ISO is it? And what exact editionid matches?
Just a heads up the tool is password protected, could you pass along an unprotected archive or the password it's self?
Modified the registry, confirmed that 0409 is set for both default & install language, but neither LTSC nor regular 10 ISO's will accept it, I also modified the registry as you suggested. Rebooted after all reg modifications just to be safe and no dice. I did have this in my registry in the language section, which was blank at the very top:
The editionid change doesn't help here, i showed you what should work with documented info. Normal Consumer ISO should simply work when same language/arch ISO is used and for 2019/2021 LTSC it needs the modified upgradematrix.xml too.
Ran the tool, used the LTSC2021 ISO to modify it, mounted & tried to install. Same result. Are we sure the extended life updates aren't interfering with it?
So there must be something special on your install. Try to update to LTSB2015 to see what happens, eventually you should be able to upgrade again to 2021 w/o any special tweak.