What is the authenticity of the hadith that prohibits recitation in the first two rak'ahs of Maghrib or 'Isha because he (the Prophet) used to recite and they also used to recite, and is it permissible to forgo recitation in a loud prayer and listen to the Imam?

Perhaps the questioner is referring to the hadith narrated by Ahmad and Abu Dawud from Ubada ibn al-Samit: "The Messenger of Allah, peace and blessings be upon him, led them in the Dawn prayer, and the recitation became difficult for him. When he finished, he said: 'I see you reciting behind your Imam when he recites aloud.' We said: 'Yes.' He said: 'Do not do so, except for the Umm al-Qur'an (Surah al-Fatihah), for there is no prayer for one who does not recite it.'"

In this hadith, there is a prohibition for the follower from reciting behind the Imam except for Al-Fatihah. Therefore, if you are a follower in a loud prayer, recite Al-Fatihah, then listen attentively to the Imam's recitation.