When using the built in product widget within Builder Theme Studio, you have the ability to set the add to cart button to not direct to the check out page and instead just add the item to the customer’s site by toggling this switch in the product box’s options tab:
Since each Shopify theme has different logic on how it shows the ajax cart, Builder can’t automatically make sure all icons (like a cart icon) are updated to reflect the addition of a product to the cart. You can however choose to make it so when a customer clicks “add to cart” the whole page refreshes, which will ensure any theme elements related to the cart will update accordingly:
