Override the minicart.js on your theme from vendor/magento/module-checkout/view/frontend/web/js/view/minicart.js

Under the initialize: function () you will see the below code

$('[data-block="minicart"]').on('contentLoading', function () {
    addToCartCalls++;
    self.isLoading(true);
});

Replace with below code

$('[data-block="minicart"]').on('contentLoading', function () {
    addToCartCalls++;
    self.isLoading(true);
    $('[data-block="minicart"]').on('contentUpdated', function ()  {
        $('[data-block="minicart"]').find('[data-role="dropdownDialog"]').dropdownDialog("open");       
        setTimeout(function() {
            $('[data-block="minicart"]').find('[data-role="dropdownDialog"]').dropdownDialog("close");
            }, 4000);
    });
});