We checked your site and found that Ajax add to cart issue caused by a large number of scripts that you have on your page https://prnt.sc/1ud0qg1 (86 scripts on the single product page)
Please, check the plugins that you installed and disable plugins that you don’t really need or could avoid using of these plugins. After that enable minification and combine options for the scripts and check the add to cart speed then.
Also, reduce the server response time https://prnt.sc/1ud19w8
