That's not just an issue with usb-c. normal usb a and b cables can have data or no data depending on how stingy the company wants to be, and you can't know until you test it
You can get pretty good guesses just by feel and length. Tiny with a super thin cable? Probably charge only.
You can get pretty good guesses just by feel and length. Tiny with a super thin cable? Probably charge only.