This is a card I've had for years at this point. The mobo is new and my cpu is less then 6 months old. I do not have another gpu to test sadly. My mobo is Asrock z790 pro rs w/ stock settings besides xmp and my cpu is i9-13900k.Motherboard and CPU?
Is this a card you've had or was this purchased used?
Generally speaking if the motherboard isn't hard set to some sort of bifurcation mode it's going to be a phsycial problem. That means it's either video card, CPU or motherboard related. If you have any other video card swapping that in would be the first thing I'd suggest trying.
Yes, I am on the latest BIOS version.Is the motherboard bios fully up to date? Maybe CPU microcode fix, and/or compatibility updates could fix this issue.
Well that means it isn't a setting because Intel 600/700 series motherboards split x8/x8.
Without spare parts to swap in the only thing I can say would be to pull the video card out and then reinsert it if you haven't already. Could also try the video card in another machine of course if that's available.