De Gea is getting old and maybe that's why Manchester United tried to decrease his salary for the next season since is a famous payer and achieved many goals for this team. It was not good to ask this from De Gea however I think it was not about salary but that's mostly because of Ten Hag, he prefers to work with the goalkeeper he had at Ajax
Initially his salary was going to be cut by 100k per week and De Gea agreed somehow Manchester United wanted to renew his contract again and here De Gea did not agree and decided to move, we don't know if he moved because his salary were lower or he felt disrespected as a legend. actually Manchester United were criticized for what they did to De Gea but their decision is fixed and does not change anything.
After all, De Gea's salary increase at that time was due to Manchester United making efforts to restrain De Gea so hat not leaving to Real Madrid. So, if at this moment De Gea's salary is lowered, then I think that's fine because after all, age will certainly affect whether a player deserves to be paid handsomely or not. After all, if De Gea still wants to be paid handsomely at a no longer young age, then De Gea can choose to play in the Saudi Professional League. Because there are clubs that play in the Saudi Professional League, they are still willing to pay a premium for legendary players who are over 30 years old.
Some players want to be paid handsomely even when they are not in their prime anymore. That's something I have seen a lot of players do. They just do not want to acknowledge that the best days of their career are behind themselves. De Gea is one of those players. I do agree that some of his failures can be credited towards Harry Maguire. But that does not change the fact that he is getting older and he is also not as good as he was before. So I think it is only right that Manchester United does not want to give him the same amount of money that they did before.