Is there a way (that does not involve the console/cheating) to see the current visibility of my secret religion?
Outside of the console or mods, I don't think there's a way to see exactly how much visibility you have. You can get an estimate of how much visibility you have via the "under suspicion" and "highly_suspect" modifiers. If you know what events/decisions raise/lower visibility, you could manually keep track of it.
Whenever a character gains suspicion, the game then checks for 3 breakpoints: 15, 25, and 40.
At 15 visibility, they gain the "under suspicion" modifier. (-0.5 monthly prestige )
At 25 visibility, they gain the "highly suspect" modifier (-1 monthly prestige, -1 monthly piety)
At 40 visibility, if the character is an independent ruler, they auto-reveal. If they're christian, they get excommunicated . If they're a devil worshiper, they gain the "known satanist" modifier (-50 general opinion, -1 monthly prestige, -3 monthly piety). If they're not a devil worshiper, they gain the "accused apostate" modifier (-10 general opinion, -0.5 monthly piety).
note: answered on version 22.214.171.124