I think PSG are too selfish and possible because their selfishness means they will lose Mbappe next season without getting anything, even though if PSG want to let Mbappe go this season they can get fresh funds to be able to bring in other players.
Sooner or later, Mbappe will definitely leave PSG and start his career with his new team, and I'm sure Mbappe really wants to join the Real Madrid team because it is possible for Mbappe to achieve everything in his football career with the Real Madrid team.
This is not entirely true because they will receive his services (the best player in the world by many) for a whole year. When PSG signed him, they thought his services were worth as much as they offered him - has anything changed since then? Mabappe began to play worse? I think no. Therefore, PSG will receive exactly what they paid for. The fact that they will not be able to resell Mbappe is a secondary issue.