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.
I think Madrid interest in Mbappe isn't the reason with his recent behaviour. Infact he had the luxury of moving to Madrid for free in the summer before PSG offered him that bumper deal and that made him to stay. If you have been reading the news about him you will see that he has being egocentric since that deal and he challenges Neymar and other teammates all the time because of the sporting previlages that's on his contract. Fast forward to the season he then noticed that both Messi and Neymar are doing better without him, and he feels he wants a move away because he prefers to be the center man of the team. But his move might be hard this time because it will cost almost 200 Million in in pounds and only Madrid could afford to cough out that much of a money now on one player, and I doubt if Madrid will actually do that deal considering how annoying it was when he rejected them last summer