The only option that makes the most sense that PSG can do at this time is to offer Mbappe to any team that is willing to pay him a high price. Mabppe has stated that he wants to stay next season or at least as long as his contract lasts, but after that he will decide his future. On Mbappe's part, I think he is also aware that there is a possibility that PSG will sell him as soon as possible to avoid future losses.
It's not even a solution. PSG can put him in the transfer market but it will be useless if mbappe will not agree in personal term to leave from the PSG to go to the its buyer.
it's not possible to force him to leave from the club without his willingness. One of the reasons why PSG is not yet putting him in the transfer market. It's caused by the transfer will not happen if mbappe is not agreed in the personal term with the new club.
So really, Mbappe's situation at PSG is very interesting. Whoever offers it higher then they might get Mbappe.
It's not as easy as you find someone that can buy your goods with high price and you give it to him. The player transfer requires many processes to be done.
You can't force him to leave the club or the last choice to terminate his contract, but he leaves with free agent.