In a way, it is partially PSG's fault because he has become too special since he became the highest-paid player in the world. Currently, he is turning into an immature person, so he needs some motivation to change his ways. It is definitely necessary for Mbappe to check his ego. In a team with Messi and Neymar, he would be able to learn and gain a lot.
I don't think that the major problem with Kylian Mbappe performance right now is about him being the highest paid player, rather might be that his mind isn't with PSG anymore since Real Madrid indicated interest about signing him last transfer window and a possible deal completion next January window transfer open. Mbappe really love to see himself play for real Madrid right from time and knowingly that a deal is set for him to play for Madrid could make him this lazy and wouldn't like to put much effort in his games at PSG.
What I read in the news is not the main problem but there is political pressure and also some unfulfilled promises to Mbappe so it might feel uncomfortable for Mbappe to continue to be at PSG if the situation is still like this, and also an option for Mbappe. Real Madrid has been rejected outright, it's not PSG's desire but only Liverpool who are the leading club for Mbappe if it's true that he will be sold in July, but what's surprising is that Mbappe's price tag by PSG is 400 million euros whether this will be able to Liverpoo and of course with a large salary for a purchase of that size, I'm not sure Liverpool will be able to make this offer too big even though Liverpool are a big team.
It will be a dilemma of course for Mbappe but I think he will make the right decision for himself with a more comfortable club.
400 million euros is such a huge amount no club will be willing to spend on one player, I don't know what the problem is, after accepting a huge deal to remain at the club he wants to leave with just a month after the deal. If the reason you say is the case then it doesn't make sense to make promises and fail to fulfil this promises. I will really love to see him make a move to Real Madrid in January.