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.
PSG fans are not in a position to blame Messi for their woes. Have they seen their team? They have a very average team; average midfield and average coach. Almost all their attacks comes through Lionel Messi.
The attack of PSG is the only functioning part of that team and it functions mainly because of Messi. He is the link between the midfield and the attack.
Messi has 20 goals and 19 assist this season, he should be having more assist if his teammates don't waste most of his passes, Mbappe included.
Its no secret that Messi is no longer the player he was at 27 but even at 36 he's still the best in the business when talking about overall football. He's human, and if he doesn't feel motivated at a particular place he cant perform like where he is motivated.