The SanDisk cards should have been supported by the R5 II, which lists specifications for UHS-II card slots and has a list of recommended card speeds in the specifications that those SD cards met.

Some cards, such as Compact Flash cards, have a mechanical lock that prevents accidental erasing or writing to the card. Insert the card into your Canon camera and turn on the camera.

And Canon's top-end 1Ds Mark III accepts both SD and CompactFlash. Now if we could just get rid of xD Picture Card from Olympus and Fujifilm and Memory Stick from Sony, we'd all be better off.