Hey Hugo,
Ok so the forearm is definitely very important in the backhand, you should keep it up and the elbow fairly high, if you image the feeling of throwing a Frisbee, the elbow is important to hinge from the elbow and push forward in the backhand shots to help keep it stable and under control.
The forearm should be the main part of the backhand which is used to generate the stroke and the wrist should come in at he end of the stroke to add spin and acceleration. Let me know if you need any other tips or info on this area 🙂
