I've found a couple of x16 nvme adapters like those:
So as a follow up to my earlier question PCIe gen3 x4 card in PCIe gen2 x8 slot - full performance possible?:
If a gen3 card that has physical x16 but only uses x4 (gen3) is put into a gen2 slot, would it use x8?
Or is that x16 just marketing and perhaps a means of holding the SSD in place more firmly than a x4 slot would?