Even if Bayern didn't win the first game, I don't think that matters for the league. Simply too good. It must be said, however, that clubs such as RB Leipzig are getting closer and closer and Dortmund can never be ruled out. I don't know if Haaland will stay.
It was expected before the start of the season that Bayern's dominance in the league would be somewhat reduced and Lipzig and Dortmund would compete for the title. In this situation, if Bayern want to win the title, thay can't lose any points against the weaker team. Bayern will have to play more carefully and better if they want to win the title.
I get that people could overreact whenever Bayern loses a game, but the reality is that Bayern 10 games total where they didn't win last year, out of 34 games, that is like 30% of the games weren't wins for them give or take. So, it is not really that shocking to see them fail to win, a team that doesn't win 30% of the time will end up like this once every three games, so that is quite common. Not like that makes them a bad team, they were still the champions with 13 point difference, not a close one honestly.
I feel like this is growing pains, they have a new manager and I believe that’s going to take a while before they could get used to his style, after all the players are nearly the same (except nagelmann brought his defensive player) and they are used to playing a certain way for so many years, when you add something to that there could be a bit of rust, but I am sure it will be fine like last year.