Real Madrid will be very hot next season just because of Mbappe's presence, but that doesn’t mean the Champions League will be easy for them. Just like you said, next season will be the last season for Guardiola at Manchester City, so he will do everything in his power to win the Champions League for the club before leaving, and we know Manchester City also has a strong squad. So I can’t really say Real Madrid will win the Champions League next season, but I know the season will be an interesting one that everyone will enjoy.
I’m also not expecting Real Madrid to win the Champions League next season because Manchester City and other clubs who are even tougher than Real Madrid are going to be fully ready for next season's Champions League. I believe next season will be a hot season, and again, I'm expecting Real Madrid to do more than they did last season because of the beast they have in their squad Now, Mbappe is a very talented player. He can do everything in his power to get the visibility he wants in Real Madrid, but what I’m also doubting is the trophy for the Champions League next season. I think it will be difficult for Real Madrid.
Real Madrid may not win the Champions league, they have the potential to do so but I can't feel Manchester City letting them have it this time. It will be very difficult because a lot of teams are currently going to improve making it hard to just give out the winning points. Mbappe will add more value to Madrid performance but it might not give the desired outcome as most people already have in mind. Every minor league could be easily won by Madrid but the Champions league will be hard to get.