I recently bought a RX 6800 XT for an "ongoing" PC build, and I probably need to just buy my new motherboard. I have 2 really old motherboards with PCIE x 16 version 1; yes, very old. The RX 6800 XT is PCIE 4.0 and from what I was reading, I thought it'd be backwards compatible. I was going to go ahead and plug it into the old motherboards to verify function of the card. One of the motherboards being a proprietary HP Pavilion motherboard would not post with the RX 6800 XT plugged in. The other not even having an error readout on the motherboard, also would not post but gave out a load beep. It posted just fine without it plugged in. So, I guess I'm just verifying that compatibility is my issue. I have a Gigabyte X570 AORUS ELITE and a Ryzen 9 5950x on order for my build, but won't be here for sometime. And also getting a new power supply to replace my 10 year old 1100 watt power supply. I don't want to damage the RX 6800 XT inadvertently. Is my issue compatibility; and is there any fear that I any damage was done to it by plugging it into a non-compatible motherboard? I'm assuming that no damage was done and that the video card will work awesomely once I get the other hardware.
If your 'really old' mobo are 'Legacy only', no option for EFI (UEFI), CSM, in Bios settings would be a problem.