You are the second user to report that Rudy. I'm utilizing ARKit, which only works on iPads with a TrueDepth camera and an A12 or later processor. So both of your devices most likely don't have a TrueDepth camera and/or an A12 or later processor. I'll fix this for the next update so that the option to enable face gestures isn't even visible in the settings on devices that don't support it.
Mike
Mike