Sia's movie, Music, is quite controversial even before its diffusion.
One of the major critics is that people such as us, with our difference invisible physically, are rarely (if not never) chosen to fill a role where the character is autistic. This situation lowers the realism of every movies concerned, and it inevitably reduces the opinion we have of this film.
That problem is present in every movies or TV series that have a character supposed to be in the spectrum, even if they are judged good, such as Atypical (even if they have been a bit better after the first season apparently, the main role still isn't done by someone from our autistic community), or Rain Man.
This is the main reason, I believe, that this movie, supposed to premiere in February, have such a bad opinion by the public, but I will still watch it, to form an opinion more detailed (let's wait and see).
Somehow, the fact that the role of a character with autism isn't done by an actor with autism makes me think of the racism done by a lot of movies because: (I will use examples of movies I have seen only)
An important number of roles of characters supposed to be black with a dark skin are played by actors who have a lighter skin, or even characters without any strict 'skin information' are played by light black actors (such as Roberto Da Costa in The New Mutants, or even Michelle Jones in the Spider-Man movies in the MCU) ;
Characters who have a given origin are often played by actors with a different origin (like Anya Taylor-Joy playing Illyana Rasputin, a Russian character in The New Mutants, or the late Chadwick Boseman playing T'Challa, an African character in Black Panther)
Another situation which happens sometimes is the fact of not casting a character with American or European origin, even if that character have an important role in the first work it appears in (another example from The New Mutants is that "Karma", otherwise named as Xi'an Coy Manh, who is a Vietnamese woman present in the New Mutants comics, is not present in that movie)
To be clear, I consider the fact of not casting someone neuroatypical for a character neuroatypical to be at the same high level of shame as racism, this is why I don't believe Sia's movie will be a good one, and it will be really difficult to make me change my opinion