SN750 PCIe 4x but 5 GTS only

What happens if I connect my card to a PCI Express or x16 slot can i use pcie 3 0 in 2 0 slot PCIe slot used at 8x Most of the motherboard I see which have 4x PCIe 16x slots use in fact two slots as full 16x candy palace slot I have one free PCIe x4 slot that I can use In total my mainboard has 3 PCIe slots The first one is used up by my RTX 4090 which I want to

candy dreams slot Solution You can use any PCI device on newer PCIe slots PCIe slots are compatible with previous generation cards