The very bad performance of Germany in World Cup can affect Bayern Munich too. Germany have many players from Bayern and look at their performances in World Cup, it is not good for Bayern when they meet PSG in Champions League.
Of course it will have an impact. First of all, Bayern can train with a full squad much earlier. Then no one will be injured either. But I would not say that the players are now playing worse at Bayern Munich. In the national team, it was not just the palyers from Bayern Munich. Hansi Flick did not manage to form a team from the individual players.
You are right, indeed Bayern Munich is a team that sends a lot of players to Germany. But in terms of games, they were better when they played at Bayern Munich than when they played in Germany. Moreover, the strategic factor will also greatly affect the form of their game. I also see that Nagelsmann and Hansi Flick differ in terms of strategy. It will have an impact maybe, but it won't be significant in my opinion.