Mo Salah penalty miss was not a benchmark in this match because Liverpool were leading 1-0, Mbappe miss was a problem because they were hunting for a goal to make the score level again. Liverpool are still unbeaten, Real Madrid finally became the victim of Liverpool's ferocity in a series of perfect results achieved in the UCL.
In my opinion, Mbappe is in a bad moment in his career, he is still struggling to adapt at Real Madrid, and now he just missed a penalty in an important game. Nothing has gone right for Mbappe at Real Madrid so far, he hasn't shone at all, that's my view on Mbappe's performance so far.
Your view of Mbappe is not wrong, but if I look at the Real Madrid team as a whole in the match, it is very clear that Real Madrid were really overwhelmed in facing Liverpool so that the level of ball possession and total shots on goal were not more than Liverpool. In addition, the formation used by Ancelotti in the match also looked unusual so that it was more directed at defense than attack so that it could make the middle area not so optimal for Real Madrid. And as a result of this defeat, Real Madrid is now in a very sacred position so that in the next match Real Madrid must be able to win in order to have the opportunity to qualify for the next round in the Champions League this season.