Also, the last time I checked, many GPUs explicitly detect + block this because they want you to pay for more expensive datacenter versions of the hardware.
A number of intel consumer CPUs support SR-IOV. The iGPU splits out to 7 "virtual functions" or pci devices to map to a VM. On latest Core Ultra's you need a 2x5 model.
My understanding is that it's trivially defeatable by configuring the hypervisor to hide itself (passthrough the real CPUID strings from the processor, ACPI/SMBIOS data/etc), and graphics drivers didn't really put any more effort into detecting beyond that. It's been years since I've been on this scene though, so my info may be out of date.
when did you check last time? I've been using gpu passthrough for more than the last ten years with different gpus from amd to nvidia to onboard intels. last few years I went back to native windows, because some games refused to run in a vm.
Did something change?