If you want something similar to fanfiction, the author of the lie I've lived, jbern, has written some original fiction as well.
This one and its sequels are pretty decent. Haven't read his other series.
Not on the level of Martin, Rothfuss, Sanderson, etc. But a good break from fanfiction that still has a similar easy to readness to it. Also it's basically superhero fanfiction just with original characters instead of the established ones.
As you have super powereds on there, may want to try:
- Confessions of a D-List Supervillain: https://www.amazon.com/gp/product/B004WE0D3E?ref_=dbs_m_mng_rwt_calw_tkin_0&storeType=ebooks&qid=1630226359&sr=8-4
Confessions of a D-list Supervillian by Jim Bernheimer, which exactly what it sounds like and is great.
Mogworld by Yahtzee Croshaw follows an npc in an mmorpg that has gained sentience. My girlfriend hated this book because I kept waking her up with my laughing.
Bad Humors by Aaron Wright is a phenomenal novella that is kind of a cross between SF, fantasy, and a Lovecraftian Mythos.