€25 million euros seems like a fair price. No matter how good Donnarumma is, no club would pay the amount PSG is asking for a goalkeeper that has got just one year left on his contract. Also, PSG should know they don't have the upper hand. If they don't sell him this summer, they would still pay his wages and lose him for free next the summer. However, if they sell him right now, they would get some money back, which can be reinvested in the squad.
Given his performance last season, perhaps €25 million is still considered cheap compared to a player who hasn't proven himself as consistently as Donnarumma. The only reason PSG would sell Donnarumma at that price is because his contract expires next season, so letting him go in that situation wouldn't be profitable for PSG. They're also not experiencing financial difficulties and are probably not like other teams who only consider profit when selling players they deem no longer necessary for their managers. Honestly, this is not what we expected because Donnarumma was a player who contributed quite a lot to PSG last season, but every decision has consequences.
Yes, they want to sell Donaroma this season, thinking about financial gain. Since PSG's contract with Donaroma will end next season, if Donaroma leaves the club next season, PSG will not get any money for this transfer. Now, there is no doubt about it, Donaroma is PSG's main goalkeeper and he plays a great role in the goalpost for PSG in every match. In that case, if PSG sells him to another club at the moment, which player will they bring to the club instead? PSG must try to bring a goalkeeper of better quality than Donaroma to their club instead of Donaroma. If PSG has any weakness in the goalkeeper position, then no matter how good they perform on the field, they may have to give up and lose. So, PSG should definitely think carefully about this matter and then decide to sell this goalkeeper to another club.