Is the wife sinful if she returns to her husband after he divorced her for the third time, and he claims he was not in his right mind when he uttered the divorce, and the Dar al-Ifta in her country issued a fatwa that the divorce did not take place?

The divorce pronounced by an intensely angry person, whose anger completely overwhelms his intellect, is not effective. The general principle is that the husband's statement regarding divorce is accepted. If he claims that he pronounced the divorce without being aware of what he was saying due to extreme anger, his statement is accepted because he knows his own condition best and is entrusted with his religious commitment. Mere doubt about his truthfulness does not prevent you from allowing him intimacy. Therefore, there is no harm for you in remaining with your husband based on his statement that he pronounced the divorce while overcome by anger, as long as you do not have certainty or strong suspicion that he is lying.