This is FSE block which can be used on Single product template and in query builder block.
It has only one simple purpose – it shows product button. It’s analog of core woocommerce “Add to cart button” block but it has much more options for styling
Most important is that you can add icons to this block, including icon which will be visible when something added to cart. You can also set button as full width and disable link which woocommerce shows after product is added to cart.
This block also has variation “Single page product button”. Difference from regular Add to cart block is that it has also Input controls and variations support. Single page product button must be used only in Single product FSE templates