My opinion of Fairy good night
It is good and solid, although I find it weird that a lot of people are calling it bad or boring. And why not liking the episode is not a bad thing, calling it bad or filler, it is just plain wrong.
1) It is an episode that explores Max as a person, his relationships with Kaalki, his friends and especially Marinette, since she has a role in his life. As ladybug and as a friend. (And this is one of the only episodes that explores the personality of a kwami and their relationship with their holder, besides Trixx. tikky, Plagg and Nooro)
2) Some people called it bad written cause Markov interacting with Kaalki. But the season has had solid writing and I find it really hard to believe they forgot the theme of "technology not being able to detect kwamis", especially after Vampigami. Also, the whole season has thrown hints that Markov have gone through changes, it is more compact and it joins in the transformation of Pegasus, it is clear that Max wants to involve Markov in his super hero persona.
3) (In this point, people in the spectrum, feel free to correct me if I am wrong). People calling Max autism forced or bad representation, for me it is just a bad argument. The two times Max autism is relevant (Wreckless driver and Fairy Good night), they pointed out that he has many tools that help him go through life in an easier way, thank you the therapist. It is obvious that the heart therapy is a recent technique, since he has only a jar with them and it seems he got one everyday. The episode is not about a crisis Max is having, but more of how he is appreciative of the support he is receiving from his support system and he relies on them to succeed in the challenges he faces. He is uncomfortable with the new changes due to his mom career (reason why the heart therapy is important to him), but he is making the effort to face those challenges.
The episode shows how strong Max is, how kind his support system is, and how the therapy has help him so much. It is a love letter to Max, even Kalki pointed out, that Max is not someone to be underestimated.