I agree with you. Ten Hag must carry out an overall evaluation and learn lessons from their loss to Rosenborg. Because this is a pre-season match so I don't think this is an embarrassing defeat. Mediocre teams usually play more passionately against top European teams and teams like Manchester United also play seriously but they often make pre-season tours to evaluate and try various variations of tactics in the game. But defeat is still defeat and Ten Hag must be able to really evaluate his squad before the English league competition starts.
Yes, it's true that defeat is still defeat. Even though it wasn't a really serious match for Manchester United and was just a test match which was usually carried out in order to prepare before the season actually started. but well, from that match, Ten Hag had to go back to improving what was lacking in the squad he built. Even in terms of pass accuracy, it seems that Man United is still quite low. And actually their back line was still quite vulnerable in this match. And yeah the point is there's a lot of work to be done ten hag. And Ten Hag will test his improvements again in the next pre-season match, namely against Rangers at Murrayfield stadium.