Are UAD-2 cards supported on PCIe x4 or x16 slots?

Using x16 pcie slot disables low package c states ASPM Alderlake pcie slot x16 if the slot is open like that, you should be good to go if it's not open, you could a) use another riser to adapt the x8 to x16, or b) pcie gpu slot A x8 card will work in an x1 slot, but will be limited to x1 speeds A x8 card will also work fine in a x4 slot It will be limited to x4 speeds

pcie 4 in pcie 3 slot Yes, a x1 card should work in a x16 slot It's good that you've got it to work in a x1 slot What else have you tried it in besides the x16 slot