They had Haaland marked with 2 sometimes 3 players, that left some huge gaps on the wings which were duly exploited. The guy only needs to stand on the penalty spot and all chaos will ensue.
Foden's goal was a perfect example. KDB had the ball and three players went with Haaland leaving Foden free on the left. This tactic might restrict the number of goals Haaland gets but it's sure going to leave loads of space for others.