Harry Maguire is quite a talented player. However, he often makes big mistakes between matches, and Harry Maguire's errors have cost Manchester United several matches. Defenders have to play very carefully. But Harry Maguire is not careful. Although he was talented, he failed to develop the talent properly. Harry Maguire was not experienced enough at 30 years old.
Harry Maguire is not totally bad and has his talent as well as weakness that must be covered by his team mates and a team tactical operation. He can play well if he is put into a system that can support him, cover his weakness and help him to show off his best strength.
In Manchester United, he does not have it and he also carries very big pressure because of his high transfer fee from Leicester City to Manchester United. His performance for England is difference than what he shown in Manchester United. However he is not a top-notch central defender and far lower quality than legendary central defenders years ago in Premier League like John Terry, Rio Ferdinand, Sol Campell.
Manchester United are no longer interested in keeping Harry Maguire in their starting XI. Even if Manchester United wanted to sell him, I don't think any big club would be interested in buying Harry Maguire at a high price. I think Harry Maguire will leave Manchester United as a free agent.
They no longer want to use Maguire but they also are facing with difficult to sell him. They don't want to release Maguire as a free player but actually want to get as high money back as possible that is impossible with all recent performances from Maguire. No big club want to spend big transfer fee to get Maguire.