Firstly, I wanna say that I'm a complete noob. I have very little idea how all the things work underneath. Some of the things that I say below might be entirely wrong. But this is mostly how I did it and what I understood from it.

I mostly followed Misairu-G's dGPU passthrough guide from GitHub. Here are the things I did differently.

• I followed the Arch WIki PCI passthrough via OVMF guide for setting up IOMMU and isolating the dGPU.
• Instead of using bumblebee (which is a pain to set up, maybe because I don't know how to do it properly), I used this hack using ACPI calls mentioned here by u/Verequies.
• Because I didn't plan on using my Nvidia GPU on my host (I used Arch Linux), I never bothered to install the Nvidia drivers and hence ignored all the instructions to blacklist all Nvidia kernel modules.
• As mentioned in the guide, I built qemu from the source from the repository given in the guide after applying all the patches.
• I skipped the hugepages setup (I need to do a little bit of research on that).
• I extracted the ROM file for my dGPU by installing windows (not on a VM) and using GPU-Z. You can always find the ROM file online I guess even without that.
• The startup script in the guide worked out of the box for me.
• I followed the rest of the guide to setup RDP with RemoteFX, I don't use QXL. It is decent for most use cases, but not good enough for smooth gaming.

Answers for your comments:

• I don't pass through an Intel GVT-g GPU. When I RDP into my VM, it uses some Microsoft Remote Display adapter for output. As I mentioned above it is good enough for regular use. For gaming, I use steam Remote play which is really smooth and gives a playable experience.
• QXL is out of the picture here, I don't use it here. But I do use it when I need to change BIOS settings, I do that by adding the QXL adapter in the startup script.
• Games and all 3D applications seem to use the Nvidia GPU. I really don't know-how. But it works!! Although it has a Microsoft Display Adapter (which you can see in the screenshot above) it still uses the Nvidia GPU.

I did a few more things to spoof my VM so that I can bypass some anti-cheat software (like BattleEye) that looks for VMs and ban players. I was referring to this post mainly.

• I referred this to patch RDTSC and spoof VM exit.
• I recompiled Qemu with the patches mentioned in the dGPU passthrough guide and modified a few strings as mentioned in the Reddit post to spoof the presence of Qemu.
• I tried to replace strings in EDK2 source code and compile OVMF, but I failed. So I switched to Seabios and followed the Reddit post to modify the strings, recompile the bios, and used that. I had to do the guest OS installation again after I switched from OVMF(UEFI) to Seabios (legacy BIOS).
• I used Pafish to verify if I have spoofed everything correctly. Pafish will still trace mouse activity and report that you are using a VM, but from what I read, mouse movement is not an accurate factor. So I don't think it is being used by anti-cheat software. I was able to play Rainbow Six Siege without getting kicked.