Actually the most likely reason is the dot projector. [br]
The DP has some kind of active optics in front of the IR/laser chip, water or impact may have damaged them and you may need to find a way to separate the optical block from the silicon part and solder a replacement module on. The chip beneath the DP must stay intact because that part is paired to the phone. [br]
This is another kind of microsurgery difficulty level repair. People can do this won’t charge for cheap even in China.