Even when Mbappe missed UCL trophy on his first season at Madrid. It won't change he has greater chance to win UCL trophy in the next season. He loves UCL trophy as he has not yet won it, but he's in a club which often dominated UCL. Why should he regret it when he failed to get UCL on his first season at Madrid?
His bad season with Madrid can't deliberate the fact he and his team will always be the favorite to win UCL in another season. He's not playing at netflix FC who never won trophy, and there's nothing to feel worry about.
Best of luck him next season by performing better under a new coach.
Oh God, after all, it's the first season, he can't complain, Real Madrid is a solid and serious team. Just look at how the separation with Carlo Ancelotti happened, in a serious and professional way without drama or venom.
I wouldn't have regretted it in his place, but i understand that we are all different.