An unrealistic out of the box signing could be Richarlison from Everton. It's unrealistic because their owner is Rich and he's in the PL so he would be expensive as fuck. But he's probably the most versatile attacker in the league, great in every position. He's fast, strong, ambidextrious, tall. brilliant in the air and doesn't shy away from pressing and tracking back all game.
Everton has been shit, but he's the only one performing this season and would probably be a lot better at City. He would probably rotate to begin with as he's born 1997 and not good enough to start just yet. He's got all the tools to be world class and I think Pep could unlock it. He'll suit in with the group as well because he's extremely humble as a result of growing up extremely poor in brazil.
He could practically be a replacement for everyone in our front 3, especially someone like Sané or fighting for a spot with Gabriel Jesus. He'd give us much needed physicality while also being great at the ball and in the air.