As we can see, you are using an additional plugin for the add-to-cart function. Try to disable AJAX add to cart option in Theme Settings -> Single product -> Add to cart.
No You can also try to enable buy now button then try to add to cart. Then pls check it will not work and as you said to remove that add to cart. So I already removed that.
Yes, I see that the plugin you use for swatches is not fully compatible with our theme. We recommend you use our theme swatches instead. They work both with AJAX and Buy now button.
It is how it works for simple products without variations. If the product has some variations, the sticky add to cart button will scroll the page to the variations form when you click it. It is how it works in our theme and we can’t change this behavior.