Is it okay to put Gen 3 SSD in my motherboards Gen 4 pcie slots?

PCIe boards can fit into slots designed for their lane configuration or higher Plugging a x4 PCIe into a x16 slot is acceptable

3 slots to see if there is any performance difference when switch between slots And, I also

candy slot game Yep PCIe cards will work on PCIe slots #1 mongoloid

can you run ddr4 in a ddr5 slot For example, inserting a PCIe card on a PCIe slot will give you PCIe performance connect to the motherboard using the PCIe x4