If PSG can win the Champions League title, it will be the most embarrassing for Mbappe. But it is an honor for Ligue 1. Everyone insults Ligue 1 as the farmer's league. Because Ligue 1 is not that competitive.
There are other good players like Messi and Neymar who left Paris Saint-Germain for another club, and Mbappé wasn't the first player to leave Paris Saint-Germain for another club, so I don't understand how Mbappé will be embarrassed if Paris Saint-Germain wins the UEFA Champions League trophy this season. Unless you aren't happy that Mbappé left Paris Saint-Germain for Real Madrid and you want Paris Saint-Germain to win the UEFA Champions League trophy so that Mbappé will regret why he ever moved to Real Madrid.