Is one who does not know that Al-Wala' and Al-Bara' are part of the creed an infidel? And is one who does not declare him an infidel after knowing this an infidel?

Ignorance that Al-Wala' wal-Bara' (loyalty and disavowal) is part of the creed does not remove one from the fold of Islam, because ignorance is an excuse in such matters. One who is ignorant is not held accountable for their ignorance, unlike one to whom the truth has reached but who did not seek it out or follow it. It is not appropriate to declare an ignorant person an unbeliever due to their ignorance of the doctrine of Al-Wala' wal-Bara', for judging someone as an unbeliever is not a trivial matter. One whose Islam has been established does not cease to be a Muslim due to doubt. A Muslim is not declared an unbeliever unless they commit a saying, action, or belief that the Quran and Sunnah, or scholarly consensus, indicate to be a major act of disbelief that expels one from the fold of Islam, and the conditions for declaring someone an unbeliever are met, and its impediments are absent.