As for K. Mbappe, I think there is no regret because going to Real Madrid is not just for the reason of hunting for the Champions League title, but also about a childhood dream club. now he is at the Santiago Bernabeu, there is no regret that all he needs to do is give his best to his childhood dream club.
It's a bit sad for Mbappe that PSG couldn't qualify for the Champions League in the past seasons. PSG management couldn't find an experienced coach like Luis Enrique earlier.
Even though Luis Enrique became Paris Saint-Germain head coach when Mbappé was still playing for Paris Saint-Germain, Paris Saint-Germain wouldn't have even qualified for the UEFA Champions League final because there were so many clubs that were performing well, and they stopped Paris Saint-Germain from reaching the UEFA Champions League. Coach was not the problem why Paris Saint-Germain failed to get through to the UEFA Champions League final when Mbappé was playing for Paris Saint-Germain; it's just that Paris Saint-Germain was unlucky in the UEFA Champions League competition.