Well yes and no. Basically, the way I understand it, he renegotiated his four year deal on a fixed salary to instead give him much less than his original salary over the first two years and then to be worth much more over the next two years, so that over a four-year period the total sum would be the same.
However, now that they are trying to sell him two years into that agreement Frenkie feels shafted despite agreeing to that contractual solution (believing he would not be forced out of the club during that four-year period). So technically, he isn’t really owed any money as Barca have paid him what they agreed to but it’s obvious that he’s been fecked over economically in what was an attempt by him to help them in their tough economic situation. So from what I understand he feels entitled to the difference between what he should have been paid originally and what he actually was paid.
By publicly stating his desire to stay he a) doesn’t risk forfeiting the loyalty bonus that he’s contractually entitled to should he leave, and b) is putting pressure on Barca to resolve the economic situation since his contract otherwise from this season puts Barca in a sticky situation in FFP terms, especially if they’re paying him a huge amount of money while not being essential to the manager’s plans.