while it might feel like you can insert a B+M SSD flipped upside down if you apply enough force, or push an M-key card into a B-key socket, not only it will not work, you will reverse the input ...

The connector on a SATA-based M.2 SSD has two notches and is known as a “B+M key”. On the PC side, the M.2 socket will almost always be an M-key connector. An M-key M.2 SSD will work just fine ...

M.2 SSDs aren’t connected to the motherboard via cables; instead they are plugged in directly to an M.2 connection socket ... SSD come equipped with B+M keys, PCIe drives make use of an M key.