Even though we all say it is not about the goals but it is certainly the only yard stick I see here that people are using to judge him, overall he has been doing just fine and the only expectations he has been short of is challenging for the top scorer Title with the likes of Lewandowski. If he had gotten that goals I doubt anyone will be saying he is on a decline, Real Madrid team thought that signing Mbappe will make them invincible and they would be higher on the table but not everyone get it that he is a player that needs time just like everyone.
Even if Mbappe already have experience from other clubs I think he need time just like anyone, Messi went to PSG and he had the worst first season there, if the greatest of all time could face such challenges then Mbappe is also not going to run a way from it either
For strikers, it is mainly all about the goals and assists. A striker who fails to score will not be highly regarded. Some critics of Robert Lewandowski claim that he cannot create his chance and only score cheap goals. But some so many young strikers waste opportunities and a good example is Nicolas Jackson. Robert is contributing immensely to the success of Barca and nobody can doubt it.
Mbappe might be skilful and have some exceptional quality, but because he is not scoring goals, fans have started complaining about his performance. Everyone thought that his presence in Madrid would bring more goals, but this has not been the case. I agree that he needs time to get used to the playing style in Spain, but he needs to improve fast because Madrid has quality players who can take his place.