Barcelona spent the end of the season very well, so now it’s not worth saying that they are in decline, especially since they have a new coach and this often gives the team a good boost. I don’t think that Mbappe is capable of somehow improving Real’s attack, especially in the form he is in now. He will have to work well with Ancelotti to improve his condition, only after that it will be possible to talk about whether he can give something to Real Madrid or not.
For now, Barcelona seems to be doing well and hopefully in the middle of the season, Barcelona won't have any more internal problems that will disrupt the performance of their players. The opponents they face have many great players, including Real Madrid, who are currently very strong and will make it difficult for Barcelona to win. Barcelona must come up with a new strategy to be able to penetrate the enemy's defense in every match that will start soon.