I am not so sure nothing is written down about not reading fiction.
I love science fiction and was told by a rabbi (not necessarily a rav, but a regular rabbi who I get advice from) that I should not read it or listen (at least not on Shabbos, not sure now, if he meant not to at all, or if he was paskening that it was assur or just not worthwhile, like studying Torah would be)) to non Jewish music (at all, but that was a suggestion, he did not say it was a halacha).
I cannot cite chapter and verse because they did not quote it to me.
I am not even saying it is definately assur, but something that may be, and it might possibly be written down somewhere.
I am just pointing out that is very easy to say “It’s not written down”.
But just saying that, does not ‘make’ it true, even if no one can give the exact quote.
I remember hearing once about a great tzaddik (might have been one of the Chabad Rebbes before he actually ‘became’ Rebbe.) who was in a beis medresh and overheard someone, saying that a certain thing he was discussing with his chavrusa, was not mentioned in the Gemara.
The Tzaddik, knew it was there and asked the person, “Do you know the entire Talmud so well, that you can say that you ‘know’, it is not in there?”.