It seems that Mbappe is ready to move to Real Madrid next year as a free agent and if this is true, it is unclear how PSG will behave. Will Mbappe make the squad? On the one hand, to put him in the squad knowing that the player is leaving is not very good, because it is not very clear how he will play? Will he give his all and even if he does, the club still knows that he will leave at the end of the season.
PSG can put young and promising players in Mbappe's place, but then a player who gets a lot of money will just sit on the bench.
In general, Mbappe has created a lot of problems for the club with his decision.
Kane seemed to want to go to Bayern, but so far Tottenham have not given permission for the transition.
If Mbappe stays, of course he will play his best in every possible game (obviously taking into account the need to rest, etc.) - it is too expensive to keep one of the strongest strikers and the most expensive player on the bench. After all, PSG are paying him for his services, so they should try to get the most for their fee. And I don't think that Mbappe created any problems for PSG - he pulled this club all these years, they should be grateful to him.
If Mbappe does his part, then we can say that he will not do anything bad for PSG. It will hurt PSG if decisions are made in the team to keep him a backup. Mbappe may want to go, that's normal. He has a career and could transfer to play for a dream team. In such a case, it is necessary to support it.