PSG have unlimited money and I am not sure if financial fair play exists in the french leagues? I know it exists in other leagues which stops rich clubs from dominating the transfer market but I know there is ways around that to because Manchester City did get away with investing millions above the limit.
Financial fair play is not league restricted, all clubs in Europe are regulated, Of course there a some loopholes in the rules and that's why PSG were able to sanction deals for both Mbappe and Neymar in the same season.
Man City are even in a better situation compared to PSG, because playing in(winning) the premier league definitely generates more revenue than in the french league.