To be honest, I didn't watch this fight.  because, there are other, more exciting matches to involve betting on. I thought, if the result of the Celta Vigo vs Barcelona match would end in a draw. however, it turned out that Celta Vigo was able to win the match even though Barcelona actually controlled 73% ball possession.
I suspect, that Xavi is just trying to experiment with rotating some of his players. for example, Erik Garcia was deployed as a quarterback, even though his original position was DC. he partners with Kassie, but in the end the combination doesn't work out the way he wants. Likewise with Sergio Roberto who played as DR, in his 15 matches as the main starter, he always underperformed. It is also possible that Xavi is selecting which players he will release in the transfer window next summer. for the wing, Ferran Torres played underperform too. only after being replaced by Ansu Fati and Dembele coming in, Barcelona's game improved. So, we can assume that this match is meaningless for Barcelona. Win or lose, it doesn't matter to them.

Different from Celta, because their position was threatened in their position, they automatically inevitably played all out. and proven. Celta can take advantage of the momentum of this fight. noted, even though Celta lost in possession, every counterattack they had was quite dangerous. technically, Barcelona is much better than the home team. but by luck, Celta Vigo was able to capitalize on its momentum and topple Barcelona. as a result, Celta Vigo is good to a safe position.

So, as you say. we agree, if Barcelona is not aiming for victory in this fight. but maybe, just evaluating his team.