Hello,
Take my apologies for the delay in answering.
Add the below code to Theme Options > Custom CSS to show the return to previous page for the mobile devices
.back-to {
display: block !important;
}
Categories on the Portfolio page are filters that display items from the chosen category on the same page, it does not go to category page that’s why if you click the “return to previous page” you stay on the same page. There is no option to change these categories to links to category pages instead of filter buttons. It’s possible only by additional customization. You can submit a customization request here.
Regards