Doesn't matter for gaming at least.
https://www.techpowerup.com/review/nvidia-geforce-rtx-5060-t...
I'll let others judge for themselves, personally I'd be tempted to get an x16 GPU since the 5800X3D is actually very near top of the line and the GPU should match the CPU imho but in general even the worst case of x8 GPU on a PCIE 3.0 motherboard doesn't seem to be the end of the world