Does a father preventing his son from performing Fajr prayer in congregation at the mosque, under the pretext that the neighborhood is unsafe and out of fear of assault, constitute a legitimate excuse for not attending the congregation?

Congregational prayer is an individual obligation, and this is the most valid opinion. The prayer of a person praying alone at home is valid when there is an excuse (such as fear of harm or illness), and he will receive the reward of congregational prayer due to his good intention. Your prayer at home is valid for the aforementioned excuse. We advise you to obey your father, and try to pray in congregation in your home, as this would waive the obligation of congregational prayer according to many scholars.