Hopefully Man United won't play that bad when the season starts. And actually in the pre-season match against Rosenborg we saw that Man United did not play with their best squad completely because in that match Man United also gave the young players the opportunity to play. So I really understand these results. But if ten Hag is able to make a good strategy then even with young players he should be able to show a better game than that.
Ha! Nothing is changing at Old Trafford as long as they still employ Erik Ten Hag.
Also, I don't know why you all are taking pre-season results too seriously. It is common for games like this to end in draws or defeats, since they are not playing a full-strength XI. Rather, the objective is for the manager to figure out what tactics will work and not work at the beginning of the season, and which players he should use for that.