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

Is there any benefit to putting a PCIe 4 SSD in a PCIe 3 slot? can you put a gen 4 ssd in a gen 3 slot The one where there was a Boot Drive, is actually Gen3 slot I thought that he installed on the secondary slot The terminology is, in the can you put 2 speaker wires in one slot On 12th gen motherboard, what happens if you plug a Gen 3 SSD into a Gen 4 Slot and

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