Sufficiently Advanced Magic (Arcane Ascension, Book 1/3, ongoing) by Andrew Rowe
Whoever reaches the top of one of the goddesses’ towers is granted a boon. In order to reach it, one needs magical abilities only given to those who pass a potentially deadly test. When Corin’s older brother took this test, he never returned. Now Corin has come of age and will face the test himself to get stronger so he can reach the top of the tower and get his brother back.
Every single character in this is well written and justified in their motives. The extensive world building is one of its strongest points, although it has been criticised for being too extensive, as we sometimes sit in on lectures about magic theory and the like. I personally love all the exposition though, makes me feel like I’m actually there and gives the reader a deep understanding of the magic system.
The character interactions, inner world’s politics and secrets we uncover along the way make it impossible to put the book down. Just finished my reread and the amount of foreshadowing and intricate details you can only pick up on the second time around was staggering. Definitely gets better every time.
Also has amazingly natural representation for queerness and neurodivergence.
Note: This series is connected to two other ones, Weapons and Wielders (book 3 was among the last reviews) and War of Broken Mirrors. I recommend starting with Sufficiently Advanced Magic and then looking up where to go from there.
Free on KU.