I remember the last season, Messi started it very well with PSG in the league and in UCL. He produced a lot of goals and assists.
There was a good chemistry between him, neymar, and mbappe.
Then, the WorldCup happened... and it changed everything.
Hostility started between France and Argentina. And the environment was literally toxic for Messi at his return for PSG after that world-cup. They didn't even congratulate him for winning the World-title. And many PSG fans were booeing him because of that.
They didn't even respect this football legend; and Messi lost some of the passion, when playing for that club; let's say it clearly.
Also, Neymar's injury happened in the wrong timing for PSG, because there was no replacement (There was no Barcola or Dembele on the bench to play on the wing).
Against Bayern in the knockout confrontation, Galtier (the coach) relied on a totally new system (5-3-2 or 3-5-2); a totally new tactic that is not familiar to the players. And bayern knew how to deal with it; especially with a Mbappe who didn't succeed at his counterattacking runs VS upamecano.
If Messi was in another club, with a better atmosphere, better coach, fans, and tactical systems that are suitable for the requirements, he would have surely done much better. No doubt about that. Football is a collective team after all, and especially if you're a 36y player, with a finite energy and resources.