Is Barcelona really strong this season? I would say a stable squad is needed to win the title. But we see in the Barcelona team, their forwards are very strong. But the midfield and defence are not that strong. Barcelona's midfield will be even weaker if de Jong leaves the team. Moreover, if the defence is not strong, Barcelona will not be able to perform well on a platform like the Champions League.
Looks like De Jong will stay with Barcelona next season. If he chooses to stay, the midfield will be stronger. barcelona have signed a defender in this summer window he is Andreas Christense, I think his presence will help the barcelona defense sector next season. barcelona have a stock of players for the position of defender. I don't think Barcelona will have a big problem in the lower or midfield because Xavi already knows which areas to improve this season before they are really ready to compete next season.
But in this case I read a news sourced from Catalan Sport which said that Barcelona reportedly had prepared a sanction if Frenkie de Jong refused to be sold to Manchester United and the punishment was to exclude De Jong from the squad for this pre-season tour.
Obviously this is the opposite of what you say and it still has all the possibilities especially United are now trying to increase their bids to bring De Jong.