How to Win a Religious Victory 100% Guarantee

Honestly, any religion based Civ will do such as India, Indonesia, etc.

If you want it to work 100%, set victory condition only to religious. This will make sense in the next step.

Have it so that there is only one civilization you're going against, then pick Kongo. They can't study religion or work towards a religious victory so that makes things impossibly easy, no matter what difficulty.

This only affects the length of the game But I highly suggest that you have small map and no city states to increases the speed of the game.

That's it! You're game should be a guaranteed win but if it isn't, please let me know so i can change it. Anyway, thanks for reading!