For me, the easiest way to install Windows 10 20H2 was to install Windows 7 from an OEM disk first. However, I used an HP OEM disk on a Dell laptop. The automatic activation of Windows 7 did not work because the vendor for the disc and laptop did not match. So I used the old KMS activation for Windows 7. It worked and then I was able to install Windows 10 20H2 on top of Windows 7 with no issue.