What is the ruling on collectively sending blessings upon the Prophet (peace be upon him) aloud after finishing the recitation of the Qur'an?

Reciting dhikr in a single, collective voice is not from the Sunnah, whether it be invoking blessings upon the Prophet (peace be upon him), or saying SubhanAllah, or Allahu Akbar, or any other form of dhikr. Abdullah ibn Mas'ud (may Allah be pleased with him) censured a group of people who engaged in such an act. Therefore, one should continue to study the Noble Qur'an and avoid the innovation of collective dhikr in a single voice.