The best solution is to sign Pep Guardiola or Ancelotti, because if they failed to bring Manchester United glory, the fans will blame the players instead of the managers, so they can survive and build Manchester United for many seasons.
Ancelotti would never want to sign for Manchester United or any other team from now on. Unless Real Madrid sacks him of course which doesn't seem likely to me. Because he has already stated that he wants to retire at Real Madrid.
Here is the source: https://x.com/FabrizioRomano/status/1795486396427178049
When it comes to Guardiola, we don't know when he will leave Manchester City for now. He has closed the door for Barcelona by a recent statement he made but maybe he might be keen on working with another big team. Even if Manchester United targets him to sign one day, they had better be prepared to build the whole squad according to his system.
Coming back to ten Hag, this might be his last season depending on team performance. I would like him to be successful though as I don't think he is a bad manager actually.