Should the Fajr prayer be repeated if one's eyes closed for a few seconds during the Tashahhud, then opened before the Imam's Taslim, and the worshiper completed the Tashahhud and made the Taslim with the congregants?

If a worshipper sleeps for a few seconds during the Tashahhud, while firmly seated, his ablution is not nullified, and his prayer is valid. This is based on what is stated in "Maṭālib ʾŪlī al-Nuhā": "A slight sleep does not harm one who is standing or sitting firmly," and in al-NNawawī's "al-Majmūʿ": "If one sleeps while firmly seating his posterior on the ground or similar, his ablution is not nullified." As for inattentiveness and daydreaming during prayer, they do not invalidate it.