What is the ruling on saying "Ameen" after reciting Al-Fatiha in prayer for both the congregant and one praying alone? And does the congregant say "Ameen" after the Imam's recitation and then after his own recitation of Al-Fatiha, considering the obligation to recite it in every rak'ah? And does one say "Ameen" in the last two rak'ahs for both the congregant and one praying alone?

Saying "Ameen" after the Fatiha is recommended for the Imam, the congregant, and the one praying alone. The proof for this is that the Prophet, peace and blessings be upon him, used to say "Ameen" and raise his voice with it, and he commanded saying "Ameen" when the Imam says it. The Sunnah is to say "Ameen" after the Imam's recitation, then to say "Ameen" again after you recite the Fatiha yourself, and to say "Ameen" in the last two rak'ahs whether you are a congregant or praying alone. Imam Al-Nawawi mentioned that saying "Ameen" is a Sunnah for anyone who finishes reciting the Fatiha, whether in prayer or outside of it, but it is more strongly recommended in prayer.