How to determine from command line if NVMe slot is gen 3 or gen 4?

how to tell how many nvme drive slots a motherboard has? m2 nvme slot PCIe slots use NVMe, which is a communication protocol that leverages the increased bandwidth to support faster NVMe SSDs, which isn't present in SATA M m2 sata slot 2 SSD? SATA vs M2 NVMe; B key, B+M key, and M key; Length A B key only works on a B slot, and the same hols for an M key and M slot

m2_1 slot I'm not really up to speed with the M2 NVME SSD slots thing I remember the good old days when you just filled drive bays