The Knight and the Moth would work with this!

love this list concept!! i recommend the wetworks miracle. it literally influenced my dreams to be about a creepy non-existent religion one night after reading

The Memoirs of Lady Trent series has a fictional religion based on Judaism which is pretty cool! These books also have fictional religions:

• The Four Profound Weaves by RB Lemberg
• Witchmark by CL Polk
• The tensorate series by Neon Yang
• Blood Over Bright Haven by ML Wang
• Apparently, Sir Cameron Needs to Die by Greer Stothers
• The Priory of the Orange Tree by Samantha Shannon
• A Stranger in Olondria by Sofia Samatar
• The Raven Tower by Ann Leckie
• The Unspoken Name by AK Larkwood
• Godkiller by Hannah Kaner
• Seraphina by Rachel Hartman
• The Affair of the Mysterious Letter by Alexis Hall

Technically also any of the Discworld novels, but if you’re just including one then I guess Small Gods would probably be the best fit? Since it’s about religion and also technically a standalone Likewise any of the books by Tamora Pierce that are set in Tortall. Maybe Wild Magic as an example? Idk

The age of empire series by Michael J. Sullivan has a fictional religion. The first one is the Age of Myth. Its not the first one he wrote in this world but the first chronologically.

Oh this is such a good niche!