Count the pins in the smaller section. 5 is M and 6 is B. I think I see 5 which would make it an M key.
Either way you can use a B&M key but the questions are:
is it enabled?
Does it support NVME, Sata, or both? (the SSD type needs to match and B&M drives tend to be Sata only)
Lastly, you will need to work out a means to secure the drive that can withstand the heat of an SSD since there is no screw hole to secure the drive down. And the main reason I think the m.2 port might not be active.