NVME PCIE SSDs Solid State Drives

Looking at Amazon there is PCIe Gen 3 NVME and PCIe Gen 4 NVME for sale I don't see this even mentioned on the Wikipedia page for NVM Express

➤ High-speed NVMe PCIe Gen3 x4 Interface:combine the next-gen PCIe Gen 3x4 NVMe interface with the latest V-NAND technology

nvme m2 slot Eight NVMe SSD slots on a PCIe x16 card Silent operation Add your own ultra-fast SSDs for Mac, Windows, and Linux

nvme m2 ssd slot For example I have two SSD bays the first one supports Gen 3 x 4 speeds the second one only supports Gen 3 x 2 speeds because there are a