The only permanent solution to Manchester United's squad would be to replace Ten Haag. Because he's been around for a long time and friendly behavior has weakened, players will only perform better if he's down. Although players may not develop a passion for the Manchester United team, it is possible to do so. Because Ten Haag's behavior is not obvious to the players, there are weaknesses, so from different angles I can understand and this will be a permanent solution. Manchester United team will perform well only if Ten Haag is replaced by a new experienced coach.
I also have an opinion that is not much different from what you said for Manchester United, because a team as big as Manchester United should be able to have a coach who has a lot of experience and tactics that he can apply to every player in the team. Not just buying players as he wants, then he just guards them without giving them good tactics in every match because in the Premier League almost all teams can be stronger if one of them plays without relying on tactics and better finishing in every match.
The problems faced by Manchester United in my opinion are very complex so far, after Ferguson retired there was not a single Manchester United coach who was able to restore the performance of consistency and also the glory of the Red Devils like the previous Ferguson era, so I think in addition to Ten Hag, Manchester United should also do a complete overhaul of the team including throwing away players like Onana, Maguire and also Antony who are indeed not able to make a huge contribution to the current club, Ten Hag is a coach who has spent a lot of money in building his current squad but the results we see now are not in accordance with the money they have spent, so indeed the main thing that Manchester United is doing at this time is to evaluate the performance of Ten Hag who actually looks incapable of coaching and also brings a lot Changes to Manchester United in recent seasons.