In general, this functionality is related to WooCommerce therefore could you please check how it works with some default WordPress themes like TwentyTwenty or WooCommerce Storefront to understand is it our theme issue or not?
also i have another issue , it appears on theme page. what to do with it ?
assets/css Template is missing. Standalone themes need to have a templates/index.html or index.php template file. Child themes need to have a Template header in the style.css stylesheet.