I don't understand why Manchester United made such a poor decision to entrust the club's affairs to the wrong set of people. While you believe Alex Ferguson might have played a role, I don't entirely agree. A retiring coach making suggestions for his replacement doesn't mean the club should have blindly followed his advice.
The club needed proper restructuring and with Ruben Amorim as head coach, Jason Wilcox as sporting director, and Christopher Vivell as director of recruitment, there may be positive changes and smarter signing of quality players that will align with Ruben Amorim's vision, making the club competitive again.
Maybe in a normal situation that could make sense, but we are talking about "Sir" Alex Ferguson here. How many Sir titled people you know that are also managers? He is the only one I can think of, which means that dude was an extraordinary situation and wasn't a normal regular manager. In which case, we could easily say that he wasn't really doing just his replacement, he wasn't giving just some suggestion, he was ordering, if you do not listen to him and also fail?
You are going to be booed every single game until you are out. Management was forced to just accept him. Thankfully, he is out of the club now and no matter what he says, the team has to figure out their own way from now out and that may actually make them better.