I temporarily switched the Theme to “Twenty Twenty-Five” as suggested the conflict test link you sent. I also disabled all plugins except WooCommerce. Neither change resolved the issue. I did notice that if you add an item to cart from the product catalog (page called categories), it successfully goes to the cart and thereafter, items can be added to the cart from the Single Product Page – even if the cart has been emptied. After clearing cookies, it returned to the behavior of not adding to the cart. So whatever is preventing the Single Product Page “Add to Cart” from working isn’t a problem if the Catalog page “Add to Cart” has previously been used and is stored in the cookies.
