If we do not enter any discount code in the coupon form on the cart and checkout pages but click the “Apply” button, the “Coupon applied” trigger will be executed. While WooCommerce displays the error “Please enter a coupon code”.
This approach is present in the new WooCommerce cart and checkout block.
It looks like you are using the old WooCommerce Cart and Checkout. The new version of the Cart and checkout page that was released a long time ago is very different, and the Apply Coupon button there is disabled by default.