Oh dear, yet another thread that's been dragged into the realms of "City are hard done by and suffer more than most" narrative. Pretty sure Bournemouth have more reasons than most to feel aggrieved consideing some of the horrendous VAR decisions that went against them as they slipped to relegation by one point and losing the club millions in the process, but you don't hear their supporters constantly claiming it's a conspiracy against them!
As for Southampton Vs Man Utd, had the non-decision gone against Southampton, would it got anywhere near the same attention or coverage? Probably not!