If Mbappe's main goal was to get an even higher salary that he is already getting now, then he would definitely not want to leave PSG in my opinion. As far as i know he is the player that is earning by far the most in europe with 72 Million € per season. That is like at least 3 times more than the other absolute world class players in europe are earning. Mbappe wants to join a club where he has realistic chances to win the Champion League in the next few years. It did not work out with PSG even though they have spent so much money for players with big names.
Now he wants to join a club like Real Madrid where it is normal to always expect to win the Champions League title, even if it means that he will earn less there. He already has way more money that he can ever spend, if he is not going completely crazy and starts to buy big private jets and islands for himself lul.
Mbappe has the potential and has emerged as top young talents recently. He has achieved so many things with France and with PSG but obviously a player has to look for his next chapter as well. It is about time for Mbappe to make a move and I really like this decision. He has been clear and it is only PSG who are not even trying to understand it at all. If PSG wanted to sell top player at top value then they should have taken the Real Madrid offer 2 years ago.
It's not about money for most players. For some players who have so many potential and has been on a spotlight, they always like the progress and Mbappe seems to me like that type of player.