That's hilarious really and I don't mean its solely done to benefit City, the referees are just incompetent. It just happened that City benefited tonight. Could be anyone.
VAR can spot:
1) Mane's armpit being offside vs Everton (wtf lol)
2) A player's finger making him offside in a frame by frame analysis
3) Shaw fouling someone on one end and calling the play back after a counter attack and possible red card for the other team
But they can't spot:
1) A player coming back from an offside position, not only coming back but actively tackling the guy who is trying to control the ball in the same phase of play