M.2 WiFi cards are “E-key” M.2 devices, while M.2 NVMe SSDs are “M-key”, and SATA SSDs are “B+M-key” M.2. A “key” on an M.2 slot prevents you from installing any M.2 device that doesn’t have the same key, though you can install devices that have additional keys - for example you can install a SATA SSD in an M.2 slot that only has an M key.



The majority of M.2 slots are M-key, but some (which only support M.2 SATA SSDs) are B+M-key, and some (which only support WiFi cards) are E-key.



You physically cannot install an E-key device directly into an M-key slot or vice versa, because the key on the socket needs to slot into the key on the device.



It is possible to get adaptors to convert an M-key slot to an E-key slot, but the inverse is very rare, because the E-key interface only supports PCIe 1x, so a SATA M.2 SSD installed in it would not work, and an NVMe SSD would be limited to 1/4 of its normal bandwidth.