Is it better to pray in congregation at home or in the mosque, if the imam of the mosque mispronounces Al-Fatiha by replacing the letter "dhāl" with a "dāl" and elongating the "hā’" in " عليهم ( عليهم )", knowing that the Maliki school of thought permits praying behind someone who mispronounces Al-Fatiha?

It is preferable to replace an Imam who makes obvious grammatical errors (laḥn jalī). If that is not possible, then praying in another mosque is more appropriate. If there is no other option but to pray behind him, then it is better to pray at home in congregation to avoid the disagreement of the majority of scholars who invalidate the prayer behind such an Imam. As for the Malikis, some of them hold that his imamate is not permissible if he changes the meaning, while others deem it initially disliked but the prayer behind him remains valid, which is the preferred view among them.