Sometimes I think the whole Lexile thing boxes people in more than it helps. A 900 Lexile just measures sentence complexity and word frequency, not content maturity. You can absolutely find genre diversity there. I was helping my younger cousin look for books at that level, and we found a sci-fi thriller about a colony ship, a contemporary novel about a kid dealing with anxiety through baking, and a historical fiction set during the Harlem Renaissance. They were all tagged for young adults and had that Lexile. The system isn't perfect—some books at 900 feel too young for a 16-year-old, while others are spot-on. The trick is to ignore the number after you've used it to filter out impossibly dense texts, and then just judge the summaries and reviews like normal.
Librarians have told me the sweet spot for many YA novels actually falls right in that 800-1000 range, which covers a huge swath of the section. You're not going to find super literary, metaphor-heavy prose there, but that's fine. The genres are all represented: fantasy with clear world-building like 'Six of Crows', lighter romance, mystery, even some accessible non-fiction memoirs. The diversity of stories is totally there; you just have to be willing to browse past the number on the back.