Is it permissible not to return a greeting in the mosque to avoid interrupting the recitation of the Qur’an, and is it obligatory to repeat after the muezzin during the Iqama, and what is the remedy for lacking devotion (khushu') in prayer and Qur’an recitation?

It is obligatory to return the greeting of peace to someone reciting the Qur’an. It is legislated to interrupt the recitation to respond to the call to prayer (Adhan) and the Iqamah.

Devotion (khushu') in prayer is a cause for success, and it is achieved by engaging in it with focus, pondering the remembrances (adhkar) and verses (ayat), and avoiding whatever distracts the mind. It is not a condition for the validity of the prayer.

Feeling that one's prayer is not accepted is a whisper (waswasah) from Satan, and it is repelled by having a good opinion of Allah.