Hmmmm... What are you talking about

Barcelona voluntarily signed a contract with him and are obliged to fulfill it, if they want to break/change it, then they either pay a penalty or negotiate with the player (it is naive to think that he will reduce his salary). They also cannot sell him without his consent.
By the way, what do you think about Olmo? Look at his injury history

Oh you got me completely wrong my friend.

Why would I think they can just simply change his current contract conditions? Of course it is impossible. But maybe I should have written it more clearly.
Anyways, I actually meant doing that
by a new contract. It seems like Barcelona doesn't intend to sell him these days. Then they can just offer a new contract and try to convince him for a lower salary. Yeah maybe it would be optimistic but maybe he would make sacrifice a little by thinking of the financial condition of the team.
When it comes to Olmo yeah I must admit he is also prone and already injured if I'm not wrong. But isn't there still a big gap between his and de Jong's salaries?
https://www.capology.com/club/barcelona/salaries/If we are talking about a future contract, then yes, there are no questions. But I don't think De Jong will stay in Barcelona, most likely the love has already passed

As for De Jong's "big" salary, it is only because he agreed to receive very little for a couple of seasons due to Barcelona's financial problems, but for it to be compensated later. In other words, he essentially gave the club an installment plan. And after that, the club repaid him with black ingratitude (they first tried to convince him to agree to a serious salary reduction, and then tried to sell him to United and thus "forget" about the installment plan).