Do dreams hold any value in Islamic Sharia, especially if they come true in reality? And what is the interpretation of a non-observant person seeing dreams that come true and through which he knows what will happen?

The true vision for a righteous person is good tidings for him, and it is from Allah. As for the one who is not committed, the truthfulness of his vision may be a gradual enticement (istidraj), and it should not be relied upon to establish a legal ruling. A disbeliever may also see a true vision, as happened with Joseph's two companions and the king of Egypt. And the vision of a believer hardly ever lies when the time draws near.