Will he be rewarded for what he did after repenting from showing off?

If a disbeliever performs a righteous deed during their disbelief, and then embraces Islam and repents, they will be rewarded for the good deeds they previously did. This is based on the Prophet Muhammad's (peace be upon him) statement to Hakim ibn Hizam: "You embraced Islam with all the good you did before." This indicates that sincere repentance restores the reward for righteous deeds that preceded a sin or disbelief.