I’m from the Bible belt and in my experience these people absolutely believe in God and heaven, but probably very little past that. These people mostly have a “vibes based” understanding of their religion but many of them believe it to their absolute core. Most don’t read the bible past the popular verses and even less actually analyze what the text is saying, but that by no means indicates a lack of belief. It’s important to remember that their actions may indicate a lack of belief in the morals they espouse, but that’s cognitive dissonance not secret non-belief.