This is never the Manchester united that I used to know, If ETH doesn't do anything concerning the goalkeeper I see Manchester going down, in my own point of view I see the team trying to make things right in teams of defence, tactics, passion to fight but the goalkeeper let them down everytime.
The best idea for Manchester united right now is to buy a new goalkeeper and start back from where they stopped. Besides is never too late for Manchester united
I remember when DDG had just joined United as a young boy under Sir Alex Ferguson. he would make quite a number of mistakes on the goal and at one point he came under heavy criticism, but that did not stop Fergie from trusting him until her turned into a very good goalkeeper. Maybe what Onana needs is some confidence now that he is at a big stage and under intense pressure.
Buying and selling players because they haven't performed after a few games won't help. Some players, especially goalkeepers, get better as they age.