What is the ruling on gathering to supplicate collectively after completing the recitation of the Holy Quran? Is it considered an innovation (bid'ah)? And was any specific supplication for the completion of the Quran transmitted from the Messenger of Allah (peace be upon him)?

There is no evidence for specifying a particular supplication upon completing the recitation of the Qur’an. Therefore, a person may supplicate with whatever beneficial supplications they wish, such as asking for forgiveness of sins, attaining Paradise, salvation from Hellfire, seeking refuge from trials, and asking for success in understanding, acting upon, and memorizing the Qur’an. It is authentically reported from Anas, may Allah be pleased with him, that he used to gather his family when he completed the recitation of the Qur’an and supplicate. As for the supplication attributed to Ibn Taymiyyah, there is no information regarding the authenticity of its attribution to him.