It's not really a loan. It's a purchase disguised as a loan with an obligation to buy - like Cuadrado's. It's a way to get around the 5 year contract term limit. It's financial engineering, not a true loan.
Essentially accounting rules spread the fee over the term of the contract, buy its capped at 5, so you can't spread it over 8. This just allows you to do that.
20 per year essentially depreciates Pogba to 0 accounting value, and then the fee for 90M is a pure capital gain for United. You'd need to likely pay a bit more, or structure the cash flow in a favourable way for United, but it isn't really a loan.
Granted you'd probably need to do something to entice them to play your FFP circumventing game. Give them 0 cost Khedira as a throw in. No FFP loss on our end, except for saved wages.