How does Civilization VI determine how many religions may exist in a given game? I've heard two primary theories: first, that the number is calculated based on the number of major civs in the game, and second, that the number is locked to the size of the map.
A forum post about Civ V claims the number was locked to the map size in that game, and it seems many base mechanics have stayed the same from V to VI.
That can't be the only factor, though. I'm playing a game right now on a Tiny map (using the default four civs) where the religion menu says that up to three religions will be allowed. However, I've been accumulating Great Prophet points for a long time, and still haven't gotten a religion. In fact, only one civ has (the one that built Stonehenge). When I check the Great People panel, the Great Prophet column just says "All people of this type have been earned." This is true even after I progress to a new tech era.
The only non-standard thing about my game is that I didn't start in the Ancient Era... I think I picked Classical, instead? I'm guessing this has an effect on the number of religions as well.
An explanation of how the game calculates the number of religions allowed per game is all I'm looking for, but some kind of table or chart would be really great for brownie points.