Xabi will succeed but he is facing selection challenges. You cannot keep a player like Vinicius Junior on the bench when he is fit. I am glad the new coach is featuring young players like Rodrygo and Arda Güler but introducing Vinicius in the second half is wrong. We saw his impact immediately when he came in, giving an assist and scoring a goal. The best solution might be letting Rodrygo leave for another club because both players (Vinicius) are too good to be on the bench.
I commend Xabi Alonso for giving young talents a chance to prove themselves by giving them a playing time. Of course, things will be too complicated for him to choose his team without being accused of favouritism. Unfortunately, there's no place for every player to play at the same time and some of them will feel offended sitting on the bench. From what I observed in their last match, Vinicius half performance would definitely keep Rodrygo on the bench.
Rodrygo seems to be still confused perhaps due to what happened last season because the anxiety is visible in his eyes. Of course, having enough playing time would restore his confidence and boost his performance. However, Xabi Alonso should pay attention to his midfield because it's too weak at the moment. Valverde is not helping matters in the midfield and it might cost them if no solution is taken immediately.