Hi Rachid,
Yes it can be difficult to keep the wrist stable during shots. I think one of the most important things is to try to keep a relaxed grip and this will help the wrist to not tighten up. Also really trying to generate the forehand drive and topspin from the lower part of your arm and hinging from your elbow can help the wrist to not bend at the end of the stroke too.
Cheers, Tom
