[oneplane]

You can fix Error 12 by using an eGPU loader in UEFI (you can just put it on a USB drive). The problem is that Windows sets the PCIe address space wrong and then it can't properly talk to the GPU anymore. It happened during one of those large Windows feature updates last year. You can find setup and documentation on egpu.io, goalque is the author. (it's called something like automate-eGPU EFI)

[alexgaribay]

Thanks for the suggestion but I've already tried that and many other reported possible fixes that didn't work in my case.

[oneplane]

Odd, the EFI loader puts the eGPU in a fixed space that always works (mainly because it no longer looks like an external GPU to the rest of the system), and Windows can't mis-configure it anymore.