I'm fairly sure that the problem Barca have is that they cannot afford to pay off De Jong's €17m deferred wages, but they also cannot afford to pay his full salary for the next season. The only two options that are financially possible for Barca are therefore:
1. De Jong transfers to an interested club (United) but gives up a large portion of his €17m deferred salary.
2. De Jong stays at Barca but takes a massive 50% pay cut.
The player is (understandably) balking at both of those options, hence the stand off.
It's basically a game of who blinks first between Barca and de Jong. The player has already had his salary reduced to €3m/season first, then €6m/season due to Covid because of his good will towards the club. Now Barca want to avoid paying him, so they are pushing him out. De Jong is open to leaving Barca but wants to see his money first, that's why he "wants to stay". He knows that Barca either pay him the money and he leaves the club, or he stays at the club and Barca will have to pay him then. But that way, Barca won't get a transfer fee for him and he will remain a big percentage on the wage bill. That's why it's likely IMO that Barca will cave in in the end, because they lose much more money if FDJ stays at the club.
Edit: Not to mention that Barca are apparently asking him to reduce his current, already reduced salary even further, if he really wants to stay. Whist trying to set a narrative in the media that they are desperate to keep him but Frenkie only cares about money.
What a pathetic club. If Frenkie has any self-pride, then he's not staying with those rats.