1. when clicking the add to cart button displays an error like the video attached, how to fix it?
2. if you access from mobile phone, The icon is not displayed. how to fix it?
I watched the video you attached and visited your website.
1) The Products behave the same on desktop and mobile. Please check the functionality by activating some default WordPress theme just to check whether the issue is with our theme or not.
2) And for the icon please provide a relevant screenshot of the specific area to check it myself and help you out accordingly.