Blaming Onana completely is actually also bad. I think there are many factors when Man United concede a lot this season. You have to remember this season there are not many Man United defenders in good shape. Many Man United players are injured. So it was purely in the team not Onana. Ten Hag's strategy also has a lot of blunders. The players made a lot of mistakes. The flow of the ball from below does not go well, possession is easily lost. When under tight pressure, Man United is always weak to protect the ball. Many players are confused about where the ball will be given. It's a classic problem but Ten Hag has to work hard to eliminate these mistakes.
Actually, the majority of players recruited by ten hag so far are good players, including their defenders, but for some reason it seems that they were only able to show good performance when they first joined and over time their performance actually declined drastically as it is today, the number of goals conceded at Manchester United at the moment of course we cannot blame individuals by Onana, But indeed with their current squad, of course, we should question, how the scheme and game strategy applied by Ten Hag so far so that they can be so slumped.