If we wait until 2024, I think it will be a bit long because what Real Madrid wants is that at the start of the season, Mbappe is already at Real Madrid to be able to dominate the game this summer. but if indeed Mbappe is retained by PSG for me it will only be in vain because Mbappe's desire to win the UCL title has long been and maybe only by joining Madrid can he achieve what he wants.
I think it will be as late as August if you ask me, because first of August means that if Mbappe hasn't extended his contract by that time, it is automatically not extended after that as well, which makes all of this rumor become real. In that case PSG will openly put him on the market, maybe even go as far as putting a value tag on him as well, if that were to happen I am sure that teams will line up to pay for it, and yes he will be very expensive and not many teams could afford it, but not like the ones who can will stop, they will offer him.
First place on that run is Real Madrid, not only because they are rich but also Mbappe would love to play for them, he has said this himself multiple times, it is his dream team since he was a kid.
Mbappe already said that he is not going to extend the contract if it is true that he sent this letter to the club bosses. What is more exciting is who else could try to get him. From Europe there are actually two clubs and that is Manchester City and Real Madrid or which other club do you think could do it? It has to be a big name and they have to have a lot of money. Mbappe wouldn't go to Newcastle. But I can't think of any other club that would be willing to pay 150 million and also a salary of 30 million net or much more than that. Haaland and Mbabbe on the same team would also be one of the strongest that the sport has seen.