Fwiw, I've had success passing through a 3090 to a windows vm without needing to dump the vbios.
I originally had a single 2080 Ti and had various issues with setting up the windows vms. I ended up following various tutorials from SpaceInvaderOne and LinusTechTips, but that didn't fully solve the issue. For me, I also needed to try some of the recommendations in https://forums.unraid.net/topic/85374-gigabyte-x570-aorus-elite-pro-wifi-ultra-tips-tricks/page/2/ as well as https://forums.unraid.net/topic/77609-guide-pass-through-primary-gpu-headless-unraid-fix-usb-panic-problems-and-linux-guest-audiovideo-stutter/ and was eventually able to pass through the 2080 Ti to the windows vm. For the 2080 Ti, I did need to dump the vbios.
I then purchased the 3090, so I currently have both a 2080 Ti as well as a 3090 in my system. I'm stubbing both and passing both to separate vms (the 3090 to the windows vm and the 2080 Ti to an Ubuntu vm). Unraid doesn't have access to any GPU, which normally in my experience requires you to dump the vbios for the graphics cards, but for me I did not have to. The 3090 worked fine without it. Though it is being passed to a windows vm that was already setup with the 2080 Ti initially w/updated drivers. So that may have helped.
Also fwiw, whenever I update the nvidia drivers in the windows vm the screen will go black and stay that way (this is the case with both the 2080 Ti as well as the 3090 for me). I've found if I just wait 10-20 minutes (> the amount of time for the update to finish) and then restart the vm, it'll work again with the driver updated. Not sure why that happens, but everything seems to work correctly after the restart so I haven't looked much further into it.
