Kylian Mbappe is an important player for PSG but they have no option than let him exits Parc des Princes stadium as a free agent. Real Madrid president, Florentino Pérez have always admire the Frenchman from day one when he was still in Monaco, but was yet to developed to the full-grown complete player this present day. Kylian Mbappe moving to La Liga would likely end up in Real Madrid because they're keen on signing him and scouting him on their rader for such long period of time. Barcelona have no interest in him, even though they did it would be a total struggle for them because they're having imbalance finances structure.
I don't think that will happen, because some time ago we also know that Mbappe received a contract extension for one season (until 2025) but with another agreement where he must be sold next season. It's probably a logical move on PSG's part because ultimately they won't be able to keep Mbappe forever at the moment.
What Mbappe wants now is not just money but more than league trophies and individual achievements. Although now he has got that but I don't think it's enough if he only succeeds with Ligue 1 because in the end there are bigger leagues like the Champions League and other much bigger domestic competitions like La Liga or the EPL that he might still be able to navigate as proof that he is one of the players to be reckoned with in the future.