What does the X4 mean in an PCIe Gen X4 NVME drive?

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

For example, inserting a PCIe card on a PCIe slot will give you PCIe performance connect to the motherboard using the PCIe x4

can you run pcie 40 in 30 slot A PCIe slot will not bottleneck the card But what CPU are you running? That might be a different story I have a I9-10900KF gig not

canada slot A PCIe graphics card can be used in a PCIe slot, but it will operate at PCIe speeds · A PCIe graphics card is backward compatible with PCIe