You can force end turn, for larger maps you can use a mod that add more pantheon (there is one in the collection)

See https://forums.civfanatics.com/threads/common-issues-please-read-before-posting.624610/

(and added a new thread with that link here)

You can also beat this by exercising your religious powers early on in the game to secure the last pantheon, it's easy to do and means you can avoid installing even more addons, you just gotta go through a specific set of game-play steps, basically all the steps that generate as much faith as possible, it is unlikely you will get a religion, but at least you'll get a pantheon and that's the important thing. Once all taken the AI will ignore pantheons completely, it's kind of dumb that you cannot permanently dismiss choosing a pantheon if one doesn't exist.