Fix Unraid Quadro Passthrough in unraid for window vm

I have a Windows Server 2025 VM running on Unraid with an NVIDIA Quadro A2000 assigned through VFIO. The card is bound in Unraid and GPU passthrough is enabled in the XML, yet every RDP attempt ends in a black screen and the GPU never appears in Device Manager.

Here is what I have already done before posting: updated the NVIDIA drivers inside the guest, checked and re-checked every VM setting, and confirmed the card works flawlessly in another system. Nothing has solved the problem, so I need an expert who knows Unraid’s KVM stack, OVMF, Q35/i440fx quirks, and the usual VBIOS-related hurdles that keep a GPU from initializing properly.

Please come in, inspect the XML, dump and patch the VBIOS if required, adjust any ACS overrides or PCIe settings, and make whatever kernel or guest tweaks are necessary so that:

• Windows Server 2025 boots with the Quadro A2000 visible in Device Manager
• RDP (and local VNC/HDMI if tested) shows the desktop instead of a black screen
• The fix survives reboots, Unraid updates, and driver updates

Document each change you make so I can reproduce it on future builds. If you’ve solved this exact issue before, I’m ready to start right away.