What is the reason for the lack of devotion (khushoo') and the feeling of tightness in the chest when reading the Quran during Umrah, and what is the solution?

Perhaps what your brother felt of胸 tightness and lack of khushūʿ (devotional humility) is a deception from Satan to turn him away from worship. Therefore, he should resist this feeling and strive against his lower self to attain khushūʿ. He should frequently remember Allah and supplicate to Him to remove what he is experiencing. He should adhere to the supplication of Dhul-Nun (Prophet Jonah): "There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers." He should seek refuge in Allah from Satan, have good expectations of his Lord, and approach his worship with diligence and enthusiasm. He should ask Allah for acceptance after completing the Umrah.