I have a soft spot for the topic of people who are dual faith. It’s weird, you know. If you’re an atheist, you get a thumbs up from me. If you’re religious with one faith, you get a raised eyebrow from me. And if you are dual faith, you get two thumbs up from me. It just feels like you’re more open-minded if you are more than one faith.
Most religions don’t explicitly say “you can’t believe anything else”, just small claims like “there is only one creator god” or “wear a hat in church” when others might say “don’t wear a hat”.
When Christianity took over Greece, the Greek gods became demonic entities and never completely went away.