M.2 PCIe PCI-E Adapter, M.2 to PCI-E3.0 X1 Expansion Card,M2 SSD ...
Is it Possible to Install a PCIe 3.0 NVMe SSD in a PCIe 4.0 M.2 Motherboard Slot?
PowerColor Readies Single-Slot, 4-way CrossFireX Ready HD 6850 ...
If you buy a PCIe 4.0 expansion card but only have PCIe 3.0 slots on your motherboard. You can still use PCIe 4.0 expansion cards with PCIe 3.0 motherboards, thanks to PCIe 4.0’s backward compatibility.
Will new RTX 3080ti cards require a PCIe 4.0 slot to work? - Video ...
Will a PCIe 2.0 work in a PCIe 3.0 slot? ... It'll surely be a bottleneck if you're using a PCIe 3.0 or 4.0 card in a PCIe 2.0 slot.