Mane was signed to replace Robert Lewandoski so it is a norm for fans to complain when he is not helping the team to win matches due to his inability to score goals but since they have returned to winning ways, I believe the players will be motivated to put up a better performance in their next matches.
Those fans should also understand that forward position is not his natural position so it will take time to adjust. He is a great player in attack and can help Bayern with great achievements but they gotta give him time to adjust to his new role and tactics that manager is giving him.
INdeed, Mane cannot replace their position of Lewandowski 100% because they are actually different positions. But at least, Bayern still has good attacking lines although after being left by Lewandowski. However, we also can see in several matches in their Bundesliga matches that Bayern really has some lacks currently, moreover after a lot or only being drawn with small clubs. Mane of course can bring some good influence to the team, moreover, he is also a very talented player, and his contribution is good enough so far, although it may not be very optimal. But in the act, his trial is really hard enough to bring this club great even after being left by Lewandowski.