Is it permissible to pray behind an imam who commands congregational dhikr aloud by one person after the prayer, and gathers worshipers every Thursday to send blessings upon the Prophet aloud with head swaying, and accuses those who rebuke him of being Wahhabis?

What the Imam does by ordering someone to raise their voice in dhikr (remembrance of Allah) after prayer, and gathering the worshippers to send prayers upon the Prophet (peace and blessings be upon him) in a collective voice with head swaying, all of that is an innovation in religion. This is based on the Prophet's (peace and blessings be upon him) saying: «Whoever introduces into this matter of ours that which is not from it, it is rejected», and his saying: «Whoever performs an action that is not in accordance with our matter, it is rejected.» As for praying behind him, it is valid as long as his innovation does not take him out of the religion, but it is preferable to pray behind an Imam who is free from innovations.