I just read this at Kingston.com
The B+M keys on an M.2 SSD allow for cross-compatibility on various motherboards as long as the appropriate SSDs protocol is supported (SATA or PCIe). Some motherboard host connectors may be designed only to accommodate M-key SSDs, while others may only accommodate B-key SSD. The B+M keys SSD was designed to address this issue; however, plugging in an M.2 SSD into a socket will not guarantee it will work, as that will depend on having a shared protocol between the M.2 SSD and the motherboard.
The M.2 SSD is fully compatible with 6th gen NUCs.
I verified the specifications of this SSD (SanDisk® X400 SSD) and it is fully compatible with the NUC. The port is M.2 2280 module (key type M) connector.
SanDisk® X400 SSD