Hello,
You will need to restrict access to RDP sessions to only devices you manage. There is no way to block this from the user side as you do not have access to their device.
If you are trying to protect IP and your data you will have to go to the extent of controlling the physical environment and the devices that access this environment. I say this, because people could in theory take out their mobile device and take photos/videos.
If this is helpful please accept answer.