I think Madrid will faced with financial difficulty because they have loss many potential player with free transfer status like Modric, Marcelo and Ramos, although sell any player like Isco, Diaz still not enough for Madrid to get Mbappe from PSG and become have looking much money if wanna get Mpabbe and keep waiting more enough money. Just waiting when Real Madrid have much money from selling many player and get Mpabbe.
I have read a rumor about this transfer, there are 6 players rumored will be sold by Real Madrid to bring Mbappe. Meanwhile, PSG is also rumored also want to release Mbappe to bring Messi. It seem very impossible for Madrid to bring Mbappe this transfer window. Barcelona have a serious financial problems, it looks like they will choose to release Messi before he becomes a free transfer player.
I would be happy if PSG takes Messi to the team. Because Messi and Neymar's pairing is really great. They understand each other well. The team will be stronger if Messi goes to PSG. But Real Madrid does not seem to be able to sign an expensive player like Mbappe at the moment. But Real Madrid need a talented and skilled striker like Mbappe.