I agree with everything that you said, Madrid has all the superstars in the world from the history and is the strongest in European competition. However, Atalanta only has average players that looks very strong due to their current form. When analyzing on a football match, you check if the teams are in form or not. Real Madrid is not in form like previous seasons which gives Atalanta the chance to win the match, because they are in form.
Well, Real Madrid actually has everything they need to become champions again in the UCL this season, just like last season. Even this season, Real Madrid has an additional star player, namely Mbappe. but we know that this team is being hit by a storm of injuries, which is why Vinicius Jr. might not even be able to play in the match against Atalanta. But hopefully he can play. But I doubt the injury recovery will be that fast. But even though Real Madrid has great players, this team is not in their best condition because of the storm of injuries. Their back line is truly unbelievable at the moment. So against Atalanta it feels like it will be quite difficult for Real Madrid this time. Because Atalanta has shown us how solid they are this season not only in the UCL but also in their domestic league, namely Serie A. I would understand if there would be many who bet on Atalanta in this match. But I'm sure many people will also try to believe in Real Madrid again in this match.