Man, you could ask me that every other week and get a different list. The algorithm giveth and the algorithm taketh away, but right now it feels like every third video is about some variation of 'dark academia' or 'romantasy.'
There's this one, 'The Atlas Six' by Olivie Blake, that's everywhere. People are obsessed with the whole morally grey, hyper-intellectual vibe. It's perfect for those 'read a book with magic and betrayal' challenge prompts. The discourse around which character you'd pick for your study group is its own whole thing on the app.
Another massive trend is the 'one bed' trope getting its own spotlight. Books like 'Icebreaker' by Hannah Grace are constantly popping up for prompts like 'a sports romance' or 'enemies to lovers.' It's pure, predictable, addictive comfort food, and challenge hosts love using it to get people out of a reading slump.
Honestly, half the fun is seeing how people creatively fit the same five super-popular books into wildly different challenge prompts. I saw someone use 'Fourth Wing' for a 'book with a dragon on the cover' prompt, which, yeah, obvious, but also for 'found family' and 'a protagonist with a disability,' which sparked some really interesting deeper chats in the comments.