Is speaking about an Imam who does not recite according to the rules of Tajweed and is disliked by people considered backbiting, knowing that there is no backbiting against one who openly commits sin?

Tajwid is of two types: obligatory and recommended. It is not permissible to follow an Imam if he violates the obligatory tajwid. As for the recommended tajwid, there is no harm in praying behind him. The dislike of the worshipers for an Imam does not affect the validity of praying behind him unless he commits something that invalidates the prayer. However, it is disliked for him to lead them in prayer if their dislike is justified. Backbiting the Imam is forbidden and is considered one of the major sins. However, it is permissible to backbite a fasiq (transgressor) under specific conditions.