Regarding Big Sur. I am running Big Sur 11.01 . The X key 16 is recognised under USB devices. if only I knew how to get KM to recognise it.
Apple T2 Bus:
Host Controller Driver: AppleUSBVHCIBCE
Headset:
Product ID: 0x8103
Vendor ID: 0x05ac (Apple Inc.)
Version: 2.06
Serial Number: 000000000000
Manufacturer: Apple
Location ID: 0x80200000
Apple T2 Controller:
Product ID: 0x8233
Vendor ID: 0x05ac (Apple Inc.)
Version: 2.01
Serial Number: 0000000000000000
Manufacturer: Apple Inc.
Location ID: 0x80100000