There is still a rumour about Messi to join an MLS team in the summer but I don't think it will be happening for Messi at least this summer.
I expect to see him for at least one more year in Europe honestly. He is just not rushing anything about his future for now. PSG seem ready to extend his contract already but he isn't thinking the same yet. I assume he would be free agent and wait for some time to make his final decision. Barcelona might be his priority but if it doesn't happen then he can continue with PSG.
I don't know if that's correct or not but even if Messi leaves PSG at the end of this season his destination is still unknown and there are many possibilities for him because unlike Ronaldo he can still play at the top team leagues, Since Messi started shining from Barcelona I think there is the possibility for him to return and then retire or he can even join the Asian teams just like Ronaldo to earn more. however, MLS can be another option for Messi as the last destination.
It doesn't feel like Messi would share the same fate as Ronaldo. I mean I don't expect Messi to join a team in the Saudi Arabia league.
I'm sure that some team in this league would be ready to offer an incredible amount of money to increase the quality more in their league. But it just feels like Messi wouldn't choose that country if he decides to leave Europe. He might prefer MLS or maybe even his first team in his career which was Newell's Old Boys. But it is much better to watch him playing for the biggest teams in Europe honestly.