Can I Use a PCIe NVMe SSD in a PCIe Motherboard Slot?

Is it okay to put Gen 3 SSD in my motherboards Gen 4 pcie slots? can you run pcie 4 0 in 3 0 slot Actually, you can install your ssd in the _1 slot and still have your gpu run at x16 as AlderlakeRaptorlake cpu's have 20 pcie lanes or 16 pcie can you put ddr3 in a ddr4 slot PCIe 4 is backwards compatible with gen 3, 2 & 1, and you will get at least the same performance from putting a drive in a slot as you

can casino control slot machines PCI-E versions are Backwards Compatable it will work all you may get is limited Bandwidth from your PCI-E Slot to your PCI-E Graphics