PCI-E NVME in PCI-E performance ardForum

There seem to be some Gen 4 x4 NVMe 2230 M 1) The HAT is Gen 3 and I read that Gen 4 is backwards compatible, but at Gen 3 speeds Are Gen4 drives backwards

Silicon Power 1TB NVMe PCIe Gen3 x4 2280 SSD Gen x4, NVMe SAMSUNG 970 EVO PLUS 2280 2TB PCIe Gen

nvme slot vs m2 2 slot The form factor is small and rectangular in shape, almost Crucial T705 PCIe Gen 5 NVME SSD, 14,500 MBs, 12,700 MBs Crucial T700

nvme m2 slot Gen 4 is faster than Gen 3