vs NVMe: What is the difference when it comes to SSDs?

Bought myself 2 NVMe M2 drives The Gigabyte motherboard has 3 slots available, marked M2A_CPU, M2B_SB and M2C_SB

While NVMe SSDs exclusively use the form factor, SATA SSDs are available in the standard form factor and the smaller and slimmer M

m2 nvme slot 2 drives are “keyed” at one end so as to prevent the end-user from inserting them in an incompatible socket PCIe NVMe drives are 'M' keyed SATA ones,

m2 slot mainboard different to the 2 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 M