Real Madrid's performance will not decline next season either; they will gain more strength because of the presence of Mbappe, although even before Mbappe came in, they were doing very well. Furthermore, I think the Champions League will be very tough this season. Arsenal, Manchester City, and other teams will want to take down Real Madrid, which won’t be a difficult thing for them. But it will be too early to predict how teams will perform next season, so let’s watch and see.
It is unlikely that Real Madrid's performance will decline, in fact I think it is almost impossible for that to happen. In fact, Mbappe's presence will make them even stronger in their attack line. with their midfield and defense, in my opinion it cannot be denied that they have a pretty good defense that is not easy for their opponents to break down. with its deadly attack line now coupled with the presence of Mbappe who clearly has quite good performance will help Real Madrid's attacks become even more deadly, Mbbape just has to play beautifully to become Real Madrid's goal scoring machine and that will make his name more known to many people and will also make he has a good story at Real Madrid.
Of course, Real Madrid's competition next season has a bigger chance, but it's true what you said is too early to predict, we just have to wait and see the best performance of each team that will compete in the Champions League next season. Every team definitely has the ambition to win, so the competition between these teams will be exciting, especially with the presence of new players who will either make the team stronger or even experience a decline in performance.