Wait, I completely missed that you've bound the card to VFIO or at least it seems that it's bound to VFIO but I didn't see any indication in the logs that the system itself bound it to VFIO, did you maybe do that manually? :
09:00.0 VGA compatible controller [0300]: NVIDIA Corporation GP104 [GeForce GTX 1080] [10de:1b80] (rev a1)
Subsystem: NVIDIA Corporation GP104 [GeForce GTX 1080] [10de:119e]
Kernel driver in use: vfio-pci
Kernel modules: nvidia_drm, nvidia
09:00.1 Audio device [0403]: NVIDIA Corporation GP104 High Definition Audio Controller [10de:10f0] (rev a1)
Subsystem: NVIDIA Corporation GP104 High Definition Audio Controller [10de:119e]
Taking a deeper look into it from what I can see you bind the card in your OPNSense VM (why?) :
-device '{"driver":"vfio-pci","host":"0000:09:00.0","id":"hostdev0","bus":"pci.4","addr":"0x0"}'