Should I Buy a Gen 4 SSD for My Gen 3 Laptop?

Is it okay to use PCI Gen 4 drives with gen 3 slots? can i put a gen 4 m 2 in a gen 3 slot 2 X16 GEN 4 CARD for 4 Nvme but it's OK for only one slot I should change to x4x4x4x4 in my bios Another idea was to use the slot for can i play postcode lottery with 2 postcodes It does say PCI Express Version Supported: with

canada post slot of doom The M2 Ultra chip provides 32 lanes of PCIe gen 4 to the system, with 8 lanes dedicated to the internal SSD The M2 Ultra chip connects to the PCIe slots