PSG has the best position, and they are lucky because they have Lionel Messi as one of their big strengths. Therefore, when there are problems, usually Lionel Messi will be included because maybe there are also many who don't like Lionel Messi's game and try to make his enthusiasm at PSG collapse by receiving a lot of pressure like that.
Of course, the PSG fans think Messi isn't giving enough/his best for the club like he does when he is on International duty with Argentina, or when he played for Barcelona, and imo i think the fans are well within their rights to think that way. When they signed Messi there was quite a lot of optimism around the club, the fans thought he was the final piece of the puzzle that could finally deliver the CL for them, but two consecutive seasons now and they've been eliminated in the RO16 stage.
Having said that, i don't think it was a good idea for the fans to boo Messi a couple of weeks ago anyway, that's not the best way to show their frustration, thus i think the Argentine world champion is going to leave PSG this summer, he does not feel loved over there and so it is better for both parties if he goes. Anyway PSG's problem isn't with a single player, it is with the entire team.
Because it seems that Messi is no longer interested in continuing to join PSG, PSG has tried to extend the contract but Lionel Messi's party is reluctant to provide an answer. And PSG fans who are aware of their game tend not to be optimal instead of hoping for it as a big power they have, but lately that's not the case. It seems that there are many factors that make the engine uncomfortable and not playing optimally, and PSG realized this quickly and were willing to release their players and take advantage of it.