I think his biggest weakness is the lack of intelligence in both the build-up phase and participating in attacking moves. He struggles to anticipate the movements of the players around him.
I'm afraid he would only thrive in teams playing on the counter where he can utilize the spaces with his pace alongside a playmaker or technical wingers.
He did well at PSG as a poacher because other players like Mbappe or Neymar were creating the spaces so Kean was always on the finishing move. He never had to participate much in the build-up phase.
At Juve, he tracks back, plays with back to goal and often on the wings which results with loss of balls and misplaced key passes.
He's not that bad, it's just a purchase for the wrong tactical setup here.