Question: are pcie slots backwards compatible?
Answer: PCIe expansion slots on your PC typically come in four flavors x1, x4, x8, x16. ... PCIe is also backward compatible. If you have a PCIe 4.0 graphics card you can use it with a motherboard designed for PCIe 3.0; however, the card's available bandwidth would be limited to the capabilities of PCIe 3.0.