I don't seem to understand what you mean by Champions League being an "unexplored territory" for Bayern Munich. If I recall correctly, Bayern has been playing the UCL since 1969, and has been qualified many times after, so what is the experience lacking here? You see, being a local champion doesn't mean you are international champion, which is what is playing out with Bayern when they compete externally. I believe the local league is too easy for them, which makes it look as if they are unstoppable.
As for Bundesliga, I hope they do not relax too much this season, Dortmund is closing in faster than thought.
While I am not the one you responded to, from what I understand we can say that Bundesliga is easy for Bayern Munich to win whereas UCL isn't. Sure they have been there all the time, but they won it rarely, they won the 2019-2020 one, and did not even reached finals since, and before that the last time they won it was 2012-2013 season.
So it is safe to say that there is a big gap between winning Bundesliga and winning UCL, and it's harder to win UCL and Bayern Munich rarely does that. They can still do it, there isn't really a way that this could change, but for the time being we can safely say that Bundesliga will be theirs but most likely that UCL won't be and that is what he was probably talking about on the message you replied to.