Ten Hag only plays his favorite players. Even though there are still several good midfielders such as Amrabat, Casemiro and Eriksen that he could use as options to play.
That is a fantastic observation about Ten Hag. If not of this point of yours, I wonder why he will not bench Onana in few matches so that he will sit up. It is as if his mistakes and inconsistencies are accepted by the coach that is why he is not making any effort to improve.
However, Ten Hag actually made some adjustments today by playing Amrabat probably due to the absence of Bruno Fernández owing to injury. On a serious note, I dont to understand why he used Naino that is obviously not suitable for this match. Now Liverpool is dominating the midfield while Manchester United seems to be more on the defensive side.