I would look at a couple of things. They changed the policy on buying so called mega stars and brought in younger more hungry kids. They got rid of a bad apple in Sanchez and Pogba knows that if he ever wants to leave that cess pit he has to perform or demand a move. Covid and his stupid wages have put a stop to a move at present anyway so he may as well play as no one can afford him.
And of course there is VAR and the officials, don't forget, in their last magnificent 3-0 thrashing of who ever, the ball went out of play before being crossed for the first goal but that didn't matter and the second was offside. With that kind of help 12 games unbeaten is quite easy to do.