Is it permissible to pray behind an imam who errs in pronouncing the letter “Lām” by elongating it, such as when he says “A-ll-ah” Akbar or “ihdina-ṣ-ṣirāṭa-l-mustaqīm”?

The person who leads the prayer (imam) should be proficient in recitation and free from errors. If an error in Al-Fatihah alters the meaning, then the validity of praying behind him is a matter of scholarly disagreement. If it does not alter the meaning, the prayer is valid. However, it is preferable for someone who recites well to lead. Among the errors that alter the meaning are reciting "an'amta" (أنعمت) with a dammah on the ta', or "al-Alamin" (العالمين) with a kasra on the lam. As for a subtle error (hidden lahn) or one that does not alter the meaning, it does not invalidate the prayer. In the takbir, one should be careful not to make additions that change the meaning, such as elongating the hamza of "Allah" or saying "Akbar" as "Akbar" (أكبار). If someone pauses slightly on the shaddah of the lam in "Allah" or the silent lam in "Al-Mustaqim," it does not change the meaning, and prayer behind him is valid.