Moving boot SSD from Gen3 slot to Gen 4 expansion card?

can you put a gen 4 ssd in a gen 3 slot   Dan candy burst pg slot

Well yeah but if you put this card in an 8x slot then only two of the SSD's would work Wouldn't it just fall back to PCIe 3 speeds?

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 PCIe Gen 4 will be compatible with PCIe Gen 5 A PCIe Gen 4 device, however, will be constrained to Gen 4 requirements when put into a Gen 5

skmbet slot 2 slots I'm looking to add 2 pcie gen 4 nvme SSDs I assume one drive will use one of the x16 lanes And the graphics card On the it says PCIESATA does that mean I cant put gen 4 there? At the moment I have a WD PC SN530 PCIe Gen3 x4 NVMe installed on slot