I've read tamer media that would still qualify as questionable. I think the real question is whether something is "NSFW" if it's written media rather than visual since it's unlikely a colleague is reading your book.

That being the case, F-Droid has its own definition for NSFW, and no reasonable definition of NSFW that doesn't specifically exclude written media or religious texts would exclude the Bible (or any Abrahamic religious text, really). It's more that those books get a pass for historical reasons than anything else.