I think you are overestimating Milan capability to score goals,you have seen them leave apart Serie A in favor of the Champions League for this season but we saw the last game they played at home against Napoli in Champions and they had just one shot on target,the goal and nothing more,it was their goalkeeper who saved at least 4 sure goals from Napoli without Osimhen and as such I believe that Napoli will have no problems qualifying further in the Champions League.The odd of 1.67 I agree with the bookies is a normal one for Napoli in this case and I do not take into consideration that 0-4 lost game against Milan,it will never happen again.
Something similar was expected when Milan played Tottenham, but in the end Milan managed to play 0-0 away. Today, Milan will most likely want to play to keep the score, against Napoli this is not a good strategy, especially since Osimhen is back in the game. The most important thing is that the Napoli players cope with their nerves, since the first game was very nervous, Napoli can win today, but for this they need not to give vent to emotions.