After repairing of water damage a proplem with camera sync with flash

This is not uncommon for water damaged phones. While the technician managed to clean the device enough to allow booting and general operation, in your case there is still something wrong with the camera/flash circuitry or modules.

I would start by removing the front camera (battery first!) to see how just the rear camera behaves with the flash. If that doesn’t help, then you will need to try a new or known-good rear camera to see if this is a “parts” problem, if not then there is a problem at the logic board level that will have to be looked at by a micro-soldering tech.