Hello, @Alessandro,
Actually, the thing is all the content comes from the WooCommerce plugin our theme is responsible for only the styling if you want to set the single product page to add to cart button like it is on the home page and on the related product page then you can easily make it by going on the XStore >> Theme Options >> WooCommerce >> Single Product Builder >> Add to Cart from there you will be able to set the styles as per your need. Here is a video for a better reference: https://streamable.com/liaq6j
Regards 8Themes Team.