can you use pcie 4.0 in 5.0 slot: PCIe 4.0 | Bo Mạch Chủ. Joint Tactical Information Distribution System - Wikipedia. Everything You Need to Know About PCIe 4.0.
PCIe 4.0 SSDs can only match the speeds of a
PCIe 4.0 slot, and PCIe 3.0 SSDs can't leap in data transfer rate and bandwidth to PCIe 4.0.
Can I Use a PCIe 4.0 Graphics Card in a PCIe 3.0 Motherboard
Slot? ... You can use PCIe cards of a lower lane width (e.g., x2, x4, or x8) in a higher lane width slot (e.g., x16).