Frenkie de Jong has the highest salary at Barcelona and the club's current financial situation is indeed getting worse which makes some players worry about their salaries which might be cut, maybe the reason Frenkie de Jong has not pressed for a contract extension is because he still has to think long about this problem or decide to move to another club that will give a higher salary, he has been with Barcelona for 6 seasons and I think that is long enough, Barcalenoa want to keep him longer but cannot force the player to stay.
If he is getting the highest salary, he may not want to renew his contract with Barcelona. If he wants a higher salary, he can transfer to another European team. I am sure he will want to get De Jong. There are many teams waiting in line to meet his transfer fee and contract. He is a very good player, I really like his style. Moreover, he is still 27 years old and very young. He is capable of performing at a high level. Maybe Barcelona should reconsider their decision.
The possibility of him getting same salary ever again is gone. Barcelona will not offer the same money again, and also no other club would offer him that much money, he is not considered that good anymore. He is decent, but nothing special, and not deserving of a salary that big, we shouldn't really consider him as someone who should be paid the highest salary in any team. The only exception would be if he goes to Saudi league and he is way too young to do something like that, he doesn't need to get better results at the moment financially, he wants to prove himself.
Staying at Barcelona requires him to accept nearly 50% pay cut, and that will not happen, he will reject the offer, and he will look for more in other teams and eventually realize that no other team offers better deal neither. These type of players are the hardest for both the team and also the player themselves, they were paid way more than what they deserve, so telling them to drop to a salary where they deserve it is hard, most of the time player will have a fake understanding of their value and think they are worth more than what they really worth, and that is because they were overpaid before.