@Jaik, you’ve already come across a thread where this is discussed (although further up, so perhaps you didn’t get to see it):
On that same thread there are some workarounds discussed, although none viable/easy to invert the color of the page yet.
The PDF viewer will come back into focus for improvements/updates once we’ve implemented everything currently on the roadmap, so hopefully next year. I’ve added your +1 to this topic for the team’s consideration.