#1 Hide update cart button
.woocommerce button[name="update_cart"],
.woocommerce input[name="update_cart"] {
display: none;
}
#2 Create a file named update-cart.js
jQuery( function( $ ) {
$('.woocommerce').on('change', 'input.qty', function(){
$("[name='update_cart']").trigger("click");
});
});
#3 Enqueue it only on cart and checkout page
// CART
function add_custom_scripts() {
if( is_cart() ) {
wp_enqueue_script( 'update-cart-js', get_stylesheet_directory_uri() . '/assets/js/update-cart.js' );
}
add_action( 'wp_enqueue_scripts', 'add_custom_scripts' );