Real Madrid and Milan both have poor defensive lines but the difference is Real Madrid overcame that weakness with their goal productivity, something that Milan still can't do in the Champions League at the moment. Referring to those conditions, I think the match will belong to Real Madrid, and they will at least win by more than one goal difference. Real Madrid may be annoyed because they were humiliated by Barcelona, therefore they will be looking for redemption after failing.
Real Madrid and AC Milan both are not in their best modes but if we compare them, Real Madrid are better than AC Milan in many things. They have more star players including super star players like Mbappe, Jude Bellingham, Vinicius; and they have better form than AC Milan. It's delusional to say a team at second position in La Liga is worse than a team at seventh position in Serie A.
Both Real Madrid and AC Milan got bad results recently but in general Real Madrid are better than AC Milan and with advantage from their home stadium, I believe they will beat AC Milan in this Champions League match.
Real Madrid will definitely be annoyed because in Laliga they have just been beaten by Barcelona and for sure in this UCL they will try to be better and definitely want to be champions again and of course winning the match against Milan will be a painkiller for Real Madrid when they was defeated Barcelona in La Liga but sometimes there could be surprises in that match, but yes, I predict that many people will favor Real Madrid to win that match.
It's an accident for Real Madrid because if you only watch the first half of El Clasico, you have no reason to think Real Madrid will lose big like actual result of that match. In Champions League, many times Real Madrid were led 0 - 2, 0 - 3 but they managed to come back. Don't underestimate Real Madrid in any match especially in Champions League where they are a most successful club in history.