Is the Imam's recitation of "Al-Mustaqeem" (المستقيم) with a Kasra on the first letter Meem in Surat Al-Fatihah considered a لحن (mistake in recitation) that invalidates the prayer?

Breaking the "Meem" in the word "al-Mustaqeem" is an obvious melodic error (Lahn Jali) that does not alter the meaning. Therefore, the prayer is not invalidated if the worshiper intentionally makes this error. However, it is disliked to pray behind someone who makes this melodic error. If the melodic error does not change the meaning, such as raising the "Ha" in "al-Hamdu Lillahi," then leading the prayer by such a person is a disliked (Makrooh Tanzeehi) act, and their prayer and the prayer of those following them are valid.