To make it work on shop page also try using below custom CSS code instead of above.

@media (max-width: 800px){
.sh-woocommerce-products .woocommerce.columns-4 ul.products li.product,
.archive.tax-product_cat #page-container  ul.products li.product,
.post-type-archive-product #page-container  ul.products li.product {
    width: 50% !Important;
}
}