"Unfilmable" just means impossible to translate into a sequence of scenes, with characters and a coherent story. For example, long internal monologues about the design of space ships, etc.

You could try, but it wouldn't be entertaining in a classical sense without deviating strongly from the source material. Animated shows would have the same problem.

You have to see this from the big picture view as a way to draw mainstream audiences for a paid streaming service. Without major drastic changes, a faithful translation of Foundation would be unwatchable for most people (most people are not into documentaries let alone fake ones), and it doesn't serve Apple's goal of getting more subscribers.