A Canticle for Leibowitz by Walter Miller, Jr.

Goodreads Storygraph

"One of the most accomplished, powerful, and enduring classics of modern speculative fiction, this is a chilling, provocative look at a postapocalyptic future. A true landmark of twentieth-century literature. In a nightmarish, ruined world, slowly awakening to the light after sleeping in darkness, the infantile rediscoveries of science are secretly nourished by cloistered monks dedicated to the study and preservation of the relics and writings of Saint Isaac Leibowitz. From here the story spans centuries of ignorance, violence, and barbarism, viewing through a sharp, satirical eye the relentless progression of a human race damned by its inherent humanness to recelebrate its grand foibles and repeat its grievous mistakes."

Oh, A Canticle for Leibowitz! What this book does not have: lesbians, swords, body horror. What this book does have: Catholicism (and how!). Yes, this is indeed a classic of Catholic science fiction, which is a thing that exists. It's quietly funny, and people will think you're smart for reading it.