Did you have any issues with efifb or some other driver grabbing the gard before vfio-pci? What are your IOMMU groups like, which chard is your boot_vga, what script or method do you use to get vfio-pci to bind with your card, what's your kernel command line and what modules are included in your initramfs?
I've struggled with getting my primary GPU to work correctly for a passthrough like this, and I ended up switching it up with the secondary because I simply couldn't get it to work properly (I'd keep getting something about "
Invalid ROM contents") and I couldn't see my boot logs until the host driver finished loading. It's really inconvenient now becuase my motherboard is designed so that having a full-size GPU in the second PCIe slot blocks 4 SATA ports out of 6, so I need to have L-shaped cables in a bunch of places to make everything work properly.