Well, a fiction book could be about a character's journey of self-discovery in a contemporary setting. Maybe they're dealing with personal challenges and growth. Another option is a post-apocalyptic story where survivors have to build a new world.
Personal growth and self-discovery make for great story topics. You can explore characters evolving and learning about themselves. Also, historical events or periods offer rich material to build a story around, giving it depth and context.
One Hundred Years of Solitude--About the loneliness and search for love
The Great Gatsby: Thoughts on the Dark Side of Society and Human Nature
3 "Three-Body"-about the confrontation between alien civilization and human civilization
Love and relationships are great topics. It could be a romantic love story, a story about friendship, or the complex relationship between family members. Mystery is also a good choice. You can create a puzzling situation and keep the readers guessing until the end. And don't forget about writing stories based on current social issues, which can make your work more relevant and thought - provoking.
How about writing a story based on a historical event but adding fictional characters and their perspectives? It combines fact and imagination and can make for a unique read. For example, a story set during the Roman Empire with made-up characters who get caught up in the politics and warfare of the time.