Don't come here often but came here after seeing the video to say this.
It's likely that the device has a bios which does not work with UEFI (UEFI and BIOS are different things), there should be an option to enable legacy support for devices with non-uefi compatible firmware. Secure boot must also be disabled for this.
PCIe spec shouldn't matter, it should be forward/backward compatible without any changes to either devices firmware.
pmccall2 got a reaction from ucmRich in Unboxing Intel's PROTOTYPE GPU