Hi Matteo,
You should first open the phone and see if the connector is still properly connected, it could’ve came loose after your latest drop. If this doesn’t fix the issue, it could either be a bad camera due to the amount drops it suffered or a motherboard fault. In this case you should hope it’s a motherboard damage. As pointed out by Jessa in one of her recent videos, Apple disables FaceID if the back camera is replaced. See here: https://www.youtube.com/watch?v=Apny-yVrZJI