I think I found a bug in the UI: We recommend to our users to use thier personal webex meeting room if they want to record themselves (teachers recording thier courses). They want to record the camera, mic and presentation.
When using a room system (Tested on deskpro, rkmini and rkpro), the "Share in call" button doesn't show up if they are alone in thier meeting room, only the "Preview" button is showing.
As soon as there is another person, the button appears. I was able to "force" the sharing using the api command, so it's not a limitation.