What should one do who experiences intrusive thoughts regarding the opening Takbir (Takbirat al-Ihram) and the Fatiha while praying behind the Imam, and doubts the correctness of his pronunciation of the letters? And does the prayer of the congregant become invalid if the Imam makes a mistake in the opening Takbir or in reciting the Fatiha due to his accent?

There is no doubt that indulging in the whispers of imams corrupts one's religion and worldly life. The default assumption regarding the prayers of Muslims and their imams is validity. Therefore, the matter of imams should be taken as valid, without extremism or obsessive whispering. One should abandon searching for errors and flaws in pronunciation. Prayer is valid behind every imam unless something that prevents following him becomes apparent. We have previously clarified the type of melodic error (laḥn) that invalidates the recitation, and the leniency granted by scholars regarding letters with similar points of articulation.