Is it obligatory to correct a grammatical error (laḥn) in Al-Fatiha that does not change the meaning, and is the prayer invalidated if the worshiper does not correct a clear grammatical error in Al-Fatiha that does not change the meaning, whether intentionally or out of forgetfulness?

The subtle error (al-lahn al-khafi) does not invalidate the prayer. The apparent statements of the scholars indicate that even if committed intentionally, it does not invalidate the prayer. Consequently, it is not obligatory to correct it if it occurred by mistake, but proper recitation should be observed. Sheikh al-Islam Ibn Taymiyyah mentioned that the subtle error or an error that does not distort the meaning does not invalidate the prayer, and that there are many recitations for Surat Al-Fatihah, and the recitation that does not invalidate the prayer is one that does not distort the meaning.