Damn. Friend, are you kidding? Mbappe is not a thing and PSG have no right to dispose of him. They can only demand the execution of a contract that expires in a year. Clubs do not "sell" players, they only take compensation for the premature termination of the contract. If you do not know this, then it is surprising to me why you write in topics about football.
So it's basically the same thing right? I see this as a form of business which contains money being transferred for the services of a player which is obviously the 'salary' of a player. And the compensation you are talking about is agreed by both clubs because the club having the ownership of the 'contract' of the player (not the player himself) is willing to terminate the contract prematurely.
In short, buying and selling.
Sorry, but these are completely different things. The rudest thing we can say using the word "sale" is that the club is selling its rights to the player's services. These rights arose from the club as a result of the signing of the contract. And then the club receives compensation if the contract is terminated ahead of schedule. But the club cannot "sell" the player anywhere in any way - it is always the player's decision. Mbappe can safely wait a year and PSG have no options to put pressure on him.