What is the ruling on praying behind an Imam who makes a mistake in Al-Fatihah by saying: {Ar-Rahmanu Ar-Rahim} with a dammah on the letter "nun," and is it permissible to change the mosque because of that?

Worshipers must repeat their prayers if they prayed behind someone who substitutes one letter for another in Al-Fatihah. Praying behind someone who replaces 'dhāl' with 'zāy' and similar substitutions invalidates the prayer, because an unlettered person is one who does not perfectly recite Al-Fatihah, and it is not permissible to pray behind him if he is able to learn. However, if he is unable to learn, his prayer is valid, and it is permissible for someone like him to pray behind him. An irregular recitation that distorts the meaning is not permissible, neither in prayer nor outside it, and whoever recites with it, his prayer is invalid.