What is the ruling on reciting the Basmala aloud in a congregational prayer, given that it is a verse from Al-Fatihah? And does the validity of the congregational prayer get affected if it is not recited aloud, based on the saying of the Prophet (PBUH): "There is no prayer without the Opening of the Book"?

Scholars are in agreement that the Basmalah is part of an verse in Surat An-Naml, and is not an verse at the beginning of Surat Bara'ah. They also agree on the validity of the prayer whether the worshiper recites it aloud or silently. The preponderant opinion is that it is a complete verse at the beginning of Surat Al-Fatihah, and at the beginning of every surah except Bara'ah; this is the view of the Shafi'is. They adduced as evidence the fact that the Companions affirmed it in the Mushaf with the Quranic script for all surahs except Bara'ah, and had it not been part of the Quran, they would not have affirmed it in that manner. It is legislated to recite it aloud when reciting Al-Fatihah and the surahs in congregational prayers, and it is also legislated to recite it silently. No one should be criticized for doing either of these.