I used to think Manchester United signed wrong players in the past, and that is why Manchester United couldn't improve their performance, but after Manchester United sold some of the players who they thought weren't good enough to play for Manchester United to other clubs, those players performed well at their new club, and a player like Scott McTominay helped Napoli to win the Scudetto. That is when I knew Manchester United's poor performance was an internal problem, and Manchester United players aren't 100% responsible for Manchester United's poor performance. If Manchester United wants a total change at Manchester United, they should improve the things Cristiano Ronaldo pointed out were the problem why Manchester United is finding it difficult to challenge for the Premier League title.
Who else should we blame for Manchester United problems because it seems like one problem is connected to another. Whether it's internal or external problems, this club has changed completely in the last few seasons. As you said, total change must start from the top, namely the Manchester United board itself, there is no common vision in rebuilding the club.
Since Sir Alex Ferguson retired as Manchester United head coach, Manchester United has been struggling in the Premier League, and the coaches that have coached Manchester United since Sir Alex Ferguson retired couldn't solve Manchester United's problems, so I think the Manchester United board and the owner are responsible for Manchester United's problems. Manchester United needs to change ownership before Manchester United fans will see the change they have been looking for in a long time.