Wanted recommendation : pcie to card

Is it okay to put Gen 3 SSD in my motherboards Gen 4 pcie slots? nvme pcie 4 0 in 3 0 slot Due to the forward and backward compatibility, a PCIe GPU will perform like a PCIe GPU card if connected to a PCIe (or in the future nvme m2 ssd slot Or all three ports will perform the same with a standard 2280 drive?? Planning on a 2 TB Samsung NVMe 980 Pro as my boot drive Link to

nvme pcie slot Kinda odd he spent nearly 4 minutes talking about the difference between Gen 3 and Gen 4