If PSG decided to stop Mbappe this season then that is very big risk because if he decides to leave next season that will be on a free transfer which would cost the club a big fortune thus losing millions of Euros, the only way forward is Mbappe to give assurance to the club that he is staying with the club for a long term basis and ready to sign a new contract, however with some recent speculations of his purported move to Real Madrid is unsettling his club, of course Real Madrid needed a striker to replace Benzema who had left the club while the club is already on the move to bid for and sign Harry Kane, however I think Real Madrid will give up on signing him for Mbappe.
When Mbappe decided not to activate his contract extension option, there were only 2 options, namely PSG had to sell him this summer at a high price or on a free transfer, of course without profit, making PSG lose big because Mbappe, when Mbappe was retained, required a sizable fee. This is also a momentum if Mbappe wants to go to Madrid because next season the place offered will already be filled by another player. He just needs to make decisions for the sake of his future which will be much better than looking monotonous at PSG.