What can I plug into a pcie x16 slot?

PCIE x8 slot, and the 3080 should be ok running on a PCIE x16 slot In practice, I would question if your Bios

For instance, larger lanes such as x16 are typically used for graphics cards When using a card or component designed for PCIe in a PCIe slot

pcieslot NVIDIA NVS 510 graphics board, Full Height Bracket , Low Profile Bracket , Four locking m-DP to DP Adapters, Four locking m-DP

pcie x4 in x16 slot current PCIe Does the Intel DX79TO motherboard support x8 devices on PCIe x16 slots? 17 · PCIe x8 NIC in PCIe x16 slot