Even before Dortmund sold Haaland it was a weak team (compared to the top ones), now it is obviously even weaker and I would not be surprised if they are moved from second place to third and maybe even fourth in the upcoming season. As for Bayern, they will not have any problems in the domestic championship, as for the Champions League, randomness is of great importance there, but they will definitely be in the group of favorites.
They are not weak but just not strong enough to win Bundesliga. It is from Dortmund, not too strong enough and the over domination of Bayern in Bundesliga. Getting the runner up position will still be a challenge for Dortmund but they can do it. Other clubs in Bundesliga are not actually stronger than Dortmund. So Dortmund will still have chance and be able to get it. It is not easy for them but they can get it.
Bayern Munich would probably still win the domestic cup even without Lewandoski and book a spot on the champions league. Then, they would need to really work in the group stages.
Mane will be a good replacement for Lewandowski and I think he is a good player for Bayern. They will be able to have a strong attacking system and score enough goals to beat opponents there. It would be enough for them to win Bundesliga. They are simply over strong there and the leave of Lewandowski does not wipe out all their strength.