So, in a fantasy setting with provably-real gods, you have:
What the gods say or do on the rare occasions they can be asked about something
Backstage church doctrine
What followers of the church actually believe
What secular authorities report about those same events
What forms of worship are allowed or encouraged
All of the above, repeated for each individual god, pantheon, splinter faction of heretics, cult of personality, cult of personality(minor demon edition), alternate form because of ancient enmity between those who worship the Volcano God and live on the north face vs those who worship the Volcano God and live on the south face, and people worshipping based on the poorly-translated Ancient Wisdom of the Cuniform Shopping List
Given all that, you can easily imagine how someone could know the gods are real and yet have some...odd...beliefs compared to the rest of their hamlet. Relationships with religion your character can have, a short list:
Major holidays only worshipper. Yes the gods exist and influence the world, so you show up to church because you're supposed to, but the absolute minimum times required because you usually have stuff to do on the rest day.
Anti-theist. The gods are real, they have measurable influence on the world, and they're also assholes who don't deserve worship. This is where your Reddit teen character ends up. Whether they have a point or not is up to you.
Believer in the gods but not the Church. Blessed X is real but the guy speaking in front of the crowd each week is just some dude and probably a politics-focused jerk. Again, whether the character has a point, and/or why the gods allow this to happen, is up to you.
Devout true believer. Fairly obvious, but you can have a lot of fun with taking this char and putting them in Situations, especially ones where their faith is pointing them in 3 different directions depending on what part of the Church matters most to them.
Person who thinks the Church has it wrong. ALSO a place for Reddit Teens. They've read the holy books, and the secular books, and the banned ravings of the Prophet Loony Lynne, and they're pretty sure the Church is full of it and the gods actually require X.
Member of a niche cult who is seeking converts
Member of a niche cult who is pretending to be ostentatiously devout so the church doesn't murder them
Member of a niche cult, running away
Non-worshipping quasi-believer. Think the average person's relationship with the Theory of Relativity, or an ancient Roman peasant who lived a continent away from the Roman Emperor. Yes, sure, their teachers taught them about the gods, and they believed the teachers, but also they have work to do and it's not like the gods are going to be showing up here affecting the stew so who cares?
Non-believer. The D&D equivalent of a flat-earther.
Formerly devout lapsed member. They used to be 100% down with the god AND the church, and then something happened, and now they refuse to acknowledge either without cursing.
Person with beliefs so odd no one can figure out if they're heresy or not. Blessed X is real, and the god of agriculture, and thus bans the eating of fish because fish aren't farmed, and will speak sometimes if you are on the brink of death so it's righteous to have your wife choke you every night until you lose consciousness in case Blessed X wants to talk to you.
Person who learned about the faith at age 5 and never updated any of their understanding of anything. Incredibly devout, but to a version of the faith that isn't actually practiced anywhere.
Person who acknowledges the gods are real, but refuses to worship because why would you worship some rando mage that happens to be powerful?
ETC. Take the pantheon(s) you developed, build a human system around them, then add 1000 years of internal politics, external politics, games of telephone with important beliefs, and lay worshippers who only moderately care. It's easy to end up with 50 ways of worshipping 5 gods and 50 more ways of worshipping other stuff that's just hanging around. And then each individual group is going to have the most insane person from your local Nextdoor participating in the discussion. Shake well, and you've got a lot of interesting stuff to dig into.
