Probably none. Just download the Windows 10 image from Microsoft and make a bootable USB stick.
It's been a long time that I reinstalled my GPD Win 2 but I don't you need drivers that aren't already available with the Windows 10 image. Except for the Intel drivers that can be updated if you want to do that.
I'm still using the Windows 10 version that came with my GPD Win 2 but with the Dutch language. Never upgraded it and probably never will. Everything that I want to run on it works and I want to keep it that way.