Real Madrid should not be expecting such impact from Mbappe straight away. Mbappe is still adapting to Spanish football. The football is very different. Ronaldo had problems adapting to the la liga when he moved from the premier league to join Real Madrid. Neymar struggled in PSG compared to he was in the Spanish League.
I don't think the coach is that much worried about Mbappé's performance because he knows it's just a matter of time. It may be due to adaptation—meaning he might not have fully adapted to La Liga's playing style yet. However, Mbappé is still doing well; he is not playing badly. He has played only four matches and has already scored two goals. Are they expecting Mbappé to score in every match? If yes, I don't think it works that way.
In fact, before fans start worrying about him, they should at least observe his performance until mid-season before they start complaining. I know that, as a great player like Mbappé, people's expectations are high, but let's just remember the season has only just started. I believe he will do much better at Real Madrid.
What Ronaldo has done in football is also possible for Mbappe to achieve, but it's just a matter of time. Currently, I am not comparing Mbappe to Ronaldo because Mbappe is not near him in club achievements, but as for the international team, Mbappe has achieved great things as well. This is not an argument, but let's just acknowledge that Mbappe is a great player and has proven it both at the club level and with the international team. Let's keep our eyes on him, as he will keep setting records too. Mbappe is still young and has a long way to go.