Liverpool defeat against Nottingham in the Premier League in no way can be used as a reference, or cannot be used as a judgment about Liverpool's badness. Because after all, the reality is that Liverpool are still quite favored in the match that will be played at the San Siro later against Milan. Based on the currently available odds, although Milan are playing at home, the odds for Milan are in the range of @ 3.60, while Liverpool are in the range of @ 1.90 and thus, I think it is clear that Liverpool are still quite favored despite playing away.
After all, basically Milan also did not start the season well in Serie A and if we compare their results in their respective leagues, then of course Liverpool is clearly better because Liverpool also has a better quality or level compared to Milan. So, Liverpool defeat against Nottingham in no way can consider Liverpool weak, because such defeats also become natural because surprises can happen anytime.
If one of the teams experiences a domestic league defeat, it is not a strong reference to say that they will have difficulty returning to their best form when they play in the Champions League. Liverpool's performance so far has been quite good, even the defeat from Nottingham Forest I think will be a valuable experience for them to be able to maximize their performance as best as possible in every match.
Indeed, Liverpool will face a strong team in their first match in the Champions League, but I see that they are still quite favored because they have quite strong strength compared to their opponents. For that, if you want to bet, look at the strength of the team and the history of matches this season, if you have doubts, it is better not to bet on the first match. Instead, we will first observe their good performance in the first match in the Champions League. But for me, of course, I am very confident that I will choose Liverpool as the winner in the match against AC Milan.