Might still be a strategy to scare the interested clubs away from snatching the goalkeeper from their hands, if their game plan is to keep him and not sell him until the one season left until his career expires. Whereas for interested clubs that wants to buy him, I doubt if any of them would want to waste such money, and better not leaving the keeper until his contract expires.
I don't think PSG wants Donnarumma to remain in the club because of some reason which includes his high wages. They have already gotten a replacement, Lucas Chevalier. Maybe they want to make money from his transfer fee. I am sure that many clubs will be scared away until the French outfit reduces the fee. His contract will expire next year, and PSG might not get any amount since he would be free to move to any club he wishes.