Man City, Bayern Munich, Arsenal, Liverpool, Leverkusen, Dortmund, Inter, AC Milan and several other candidate teams will continue to be obstacles for Madrid. But regarding probability, of course Mbappe arrival is a plus point, but as you said, that doesn't mean Madrid will easily win the Champions League trophy next season. For me now I am looking forward to how far this club will prepare itself to give its best.
Most people also really want to see other teams be better prepared when they have to face Real Madrid in the Champions League because such a complicated and fierce match will always be a memorable moment and that's what the audience actually likes more than an easier victory for one team. Because last season Real Madrid also struggled when they reached the final even though in the end Real Madrid became the champion because their mentality was really ready for it.