add_action('wp_head', function () {

?><style>
    .woocommerce button[name="update_cart"],
    .woocommerce input[name="update_cart"] {
      display: none;
    }
  </style><?php

        });

        add_action('wp_footer', function () { ?>
  <script>
    jQuery(function($) {
      let timeout;
      $('.woocommerce').on('change', 'input.qty', function() {
        if (timeout !== undefined) {
          clearTimeout(timeout);
        }
        timeout = setTimeout(function() {
          $("button[name='update_cart']").removeAttr("disabled");
          $("[name='update_cart']").trigger("click"); // trigger cart update
        }, 1000); // 1 second delay, half a second (500) seems comfortable too
      });
    });
  </script>
<?php

        });