所以主要的问题是我的逻辑表达。当我们使用||（OR）时，如果$a or $b为true，它将返回true。而如果我们使用&&（AND），如果两个$a and $b都为真，它将返回true。
我还确保循环遍历购物车项目，检查运输类，并单独添加变量。这使我的第一个表达式无效$quantity_bottle < 6 && $quantity_gin < 6 && $quantity_box < 1，但我的第二个表达式$quantity_gin == 2 && $cart_totals < 600需要。为了使我的第一个表达式工作，我添加了一个新的变量，计数瓶数量和杜松子酒瓶数量的总和。

// Loop through cart content and add to specified shipping classes
foreach( $package['contents'] as $item ) {
    if( $item['data']->get_shipping_class_id() == $class1 ){
        $quantity_bottle += $item['quantity'];
    }
    if( $item['data']->get_shipping_class_id() == $class3){
        $quantity_gin += $item['quantity'];
    }
    elseif (  $item['data']->get_shipping_class_id() == $class2 ) {
        $quantity_box += $item['quantity'];
    }
}
// Variable counting gin and other bottles
$total_bottle_quantity_cart = $quantity_gin + $quantity_bottle;

所以条件是：if (($quantity_bottle < 6 && $quantity_gin < 6 && $quantity_box < 1 && $total_bottle_quantity_cart < 6 ) && !($quantity_gin >= 2 && $subtotaltax > 600 ) )
完整代码如下：

/* Hide free shipping unless minimum of 6 bottle or 1 box is selected, or if 2 gins and under 600 cart total */

add_filter( 'woocommerce_package_rates', 'hide_free_shipping_method', 10, 2 );
function hide_free_shipping_method( $rates, $package )
{
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;
    // Shipping class to check for
    $class1 = 132; // shipping class for bottles
    $class2 = 131; // shipping class for boxes
    $class3 = 142; // shipping class for gin bottles

    // Shipping method to hide
    $ShipMethod_key_ids = array('free_shipping:7'); // free shipping
    // Get cart subtotal of items in the cart incl. tax, as a number
    $subtotal = WC()->cart->get_subtotal(); // Get cart subtotal value
    $subtax = WC()->cart->get_subtotal_tax(); // Get cart subtotal value tax
    $subtotaltax = $subtotal+$subtax; // calculate cart subtotal value with the tax added
  
    // Keep track of the quantity of items with the specified shipping class
    $quantity_bottle = 0;
    $quantity_gin = 0;
    $quantity_box = 0;
  
    // Loop through cart content and add to specified shipping classes
    foreach( $package['contents'] as $item ) {
        if( $item['data']->get_shipping_class_id() == $class1 ){
            $quantity_bottle += $item['quantity'];
        }
        if( $item['data']->get_shipping_class_id() == $class3){
            $quantity_gin += $item['quantity'];
        }
        elseif (  $item['data']->get_shipping_class_id() == $class2 ) {
            $quantity_box += $item['quantity'];
        }
    }
    // Variable counting gin and other bottles
    $total_bottle_quantity_cart = $quantity_gin + $quantity_bottle;
  
    // If there are less than 6 bottles, 6 gins, 1 box and less than 6 total bottles
    // or 
    // if gin quantity is not bigger than or equal to 2 and subtotal less than 600 
    // hide the shipping method
    if (($quantity_bottle < 6 && $quantity_gin < 6 && $quantity_box < 1 && $total_bottle_quantity_cart < 6 ) && !($quantity_gin >= 2  && $subtotaltax > 600 ) ) {
        foreach( $ShipMethod_key_ids as $method_key_id ){ 
            unset($rates[$method_key_id]);
        }
    }
    return $rates;
}