No matter how bad the players in a club is a good coach will turn them into good and average players the main problem with Manchester United has been a lack of quality coaching staff United has not been fortunate in getting good coaches that understands the strength and weaknesses of their players
What Manchester United experienced last season should be a valuable lesson for them, allowing them to take unique steps to address the team's remaining weaknesses, including recruiting a better coaching staff. Players should generally avoid personal egos in any match, allowing them to carry out the coach's instructions correctly and on target. So, the problem isn't limited to one area, but rather encompasses several areas across the Manchester United team, and this must be resolved as quickly as possible before next season begins.
I wonder why you still believe that Manchester United problem was or is coaching, while they have tried so many coaches. The problem of Manchester United is lack of quality and dedicated players which I think would be solved this time around. For instance, a player like Rashford is a good player but not dedicated, likewise some other players and again there was no competition in the team. Everyone is almost certain of their wing and jersey, so no one was doing anything extra to impress anyone.
Another problem with Manchester United has been weak player and coach relation. This disstablizes the team and making some players and old boys align with one side of the divide.
We shouldn't downplay poor infrastructure and poor staff management.