This is bullshit
The notion of fair competition exists in many examples of real life, it is what free-market economy is based on and why it has regulations to safeguard it from monopoly or oligopoly. It is embedded in the idea of sportsmanship as in you don't cheat by for example taking doping.
The whole idea of financial fair play is to adress the issue of financial doping. Which is essentially what PSG and other clubs like City are guilty off using. You simply get money from your owner which allows you to grow much faster and become much bigger than possible for any other club of equal size and resources. It is simply unfair. Now you people keep calling it investments, but it is not investing money, you inve'st money because you want to see a return on investment. Now United owners, they are investers, they have already gotten much more money out of the club than they initially invested in it and the club is run like a business that has to make money and can only spend money that it has made. PSG and City are not run like that at all. If they were you could never afford transfers like that of Neymar or even most of the other transfers you did ever since you were bought by Qatar. Those rich owners they don't invest, they just want to own a football club and show the world how rich and powerfull they are by doing so and they are not expecting to see a financial return from that all. So it is not investing, it is financial doping. And the only thing that made PSG or City great is that they were the lucky ones to be purchased like winning a lottery.
Next to it being unfair for other clubs, it is also highly unsetteling for the transfermarket (yea inflation is natural but the way transfer prices are going is hyper inflation and also not sustainable) and it is simply a bad example of how to run a football club as it is clearly a non-sustainable businessmodel. So it makes perfect sense that to protect other clubs UEFA would have financial fair play rules only it seems they are not effective at all currently.