It is permissible to leave the congregation if the imam prolongs the prayer in a manner that contradicts the Sunnah, and there is no other congregation available.

Question : We begin first with the imam prolonging the prayer beyond the Sunnah. If the imam prolongs it more than the Sunnah, and there is no congregational mosque nearby, then if this mosque prolongs the congregation more than the Sunnah, he has the right to abandon the congregation.

Answer : Is that clear? The evidence is the story of Mu'adh ibn Jabal when a man left the prayer with him because he prolonged the prayer, and the Messenger of Allah (peace and blessings be upon him) agreed with the man’s action. For this reason, he did not rebuke the man, but rather rebuked Mu'adh. So if this man does not adhere to the Sunnah and prolongs it more than the Sunnah, the followers have the right to leave him. Yes.