Actually, the current Barcelona squad already has a good mentality for the Champions League competition, but with the style of play given by Xavi, it certainly won't match his opponents in this European competition. Xavi should have been able to learn from his senior who is currently coaching Manchester City, namely Pep Guardiola, who no longer uses the tik taka strategy because this game cannot be used in the modern football era as it is now.
Pep Guardiola always uses tight pressing to find box to box gaps for his players to be able to achieve precise attacks and that is why Manchester City can win the Champions League this season. Xavi must immediately evolve with his players so as not to be left behind by his competitors, especially Real Madrid, who will not be playing anymore to be able to win the Champions League title again.
Barcelona has injury problems in the group phase of the 2022-2023 Champions League season, they don't have a strong defense because several players are absent due to injury. Xavi also tends to play Alonso as a left back even though basically they have Alba and Balde, but sometimes Alonso is played as a centre-back. Out of 6 matches, Barcelona were only able to win 1 match and that was when they beat Viktoria Plzen 5-1.
You can't compare the depth of Barcelona's squad to Manchester City's. Xavi doesn't have players of the same quality as Manchester City, so even if Pep Guardiola is coaching Barcelona at the moment, this problem can't be solved either. Xavi has built a strong team, but he hasn't had success in the Champions League or the European stage. There is still a lot of hope about him in the coming seasons, so whoever is a Barcelona supporter at the moment just needs to be patient.