What should one do who is trying to learn Arabic and has recently converted to Islam, and cannot pronounce some of the letters of Al-Fatiha correctly, despite their attempts to correct them? And is their prayer invalidated because of that?

Recitation of Al-Fatihah is a pillar of prayer for the Imam, the congregant, and the individual praying alone. Whoever prays without reciting the Mother of the Qur’an, their prayer is incomplete. If recitation is difficult for someone, they must learn. If they are unable, then it is waived for them. Whoever is completely unable to recite it, it suffices for them to say: "Subhan Allah, wal-hamdulillah, wa la ilaha illa Allah, wa Allahu akbar, wa la hawla wa la quwwata illa billah" (Glory be to Allah, and praise be to Allah, and there is no god but Allah, and Allah is the Greatest, and there is no power or strength except with Allah). If they are able to recite part of it, they must recite what they can and repeat it for the number of verses in Al-Fatihah, adding tasbeeh (glorification), tahmeed (praise), takbeer (magnification), and tahleel (proclamation of God's oneness). As for errors in reciting Al-Fatihah that do not alter the meaning, they do not invalidate the prayer. However, errors that alter and invalidate the meaning invalidate the prayer if the person is aware, but if they are ignorant, their prayer is not invalidated. It is advised to strive in learning and practicing, and to listen to the Qur’an from skilled reciters. There is no need for worry or repetitive re-readings that open the door to obsessive doubts (waswasah).