Calculate subtotal on quantity increment on single product page in WooCommerce

Solution:

Use the following var qty = $( this ).val(); in an if condition. If greater than 1..

So you get:

function action_woocommerce_after_add_to_cart_button() {
    global $product;
    
    echo '<div id="subtot" style="display:inline-block;"><span></span></div>';
    
    $price = $product->get_price();
    $currency = get_woocommerce_currency_symbol();
    
    wc_enqueue_js( "      
        $( '[name=quantity]' ).on( 'input change', function() {
            var qty = $( this ).val();
            var price = '" . esc_js( $price ) . "';
            var price_string = ( price*qty ).toFixed(2);
            
            // Greater than
            if ( qty > 1 ) {
                $( '#subtot > span').html( 'Total: " . esc_js( $currency ) . "' + price_string );
            } else {
                $( '#subtot > span').html( '' );                
            }
        }).change();
    " );
}
add_action( 'woocommerce_after_add_to_cart_button', 'action_woocommerce_after_add_to_cart_button', 10, 0 );