Actually, Barcelona's game in this match was quite dominant, especially in the first half, but unfortunately their game was not very well organized. Many of the opportunities they get are just wasted. But in the second half El Barca's game was so chaotic, that Bayern immediately punished them. I see there are some technical things that Xavi needs to improve immediately, up front, Raphinha is not very effective, he is too hasty in opening shots, so Lewandowski's role is not very visible. Then the midfield also didn't look very creative and the most chaotic in defence, Christensen and Araujo were really very fragile in the second half, making it very easy for the Munich attack to penetrate. I believe this defeat is an important note for Xavi to immediately fix his squad.
Yes they had a lot of chances but unfortunately lewandowski couldn't maximize his chances. With this result adding to Barcelona's bad record against Munich which always loses, statistics show Barcelona's superiority both in ball possession and chances, Barcelona's dominance is destroyed with two goals from Munich scored by Lucas Hernandez and Sane.
The defeat in Bavaria was the first for Barcelona this season and it looks like Xavi has plenty of records to correct his squad.
As for Bayern, Nagelsmann managed to make his squad win this match, the rotation of players and the change in strategy that he did were quite effective.