Snippet to hide WooCommerce shipping methods if items of a specific shipping class is not present in the cart. Supports PluginHive Shipping Plugins: https://www.pluginhive.com/product-category/woocommerce-plugin/woocommerce-shipping/

functions.php

// Snippet to hide WooCommerce shipping methods if items of a specific shipping class is not present in the cart
add_filter('woocommerce_package_rates',     'xa_hide_shipping_method_when_shipping_class_product_is_in_cart', 10, 2);
function xa_hide_shipping_method_when_shipping_class_product_is_in_cart($available_shipping_methods, $package){
    // Shipping class IDs that need the method removed

    $shipping_classes = array(
        'free-shipping',         
    );
    $shipping_services_to_hide = array(
        'wf_shipping_usps:D_PRIORITY_MAIL',
        'wf_shipping_usps:D_EXPRESS_MAIL',
        'wf_shipping_usps:flat_rate_box_priority'
    );
    $shipping_class_exists = false;
    foreach(WC()->cart->cart_contents as $key => $values) {
        if (in_array($values['data']->get_shipping_class() , $shipping_classes)) {
            $shipping_class_exists = true;
            break;
        }
    }

    // Negation of shipping class exists.
    if (!$shipping_class_exists) {
        foreach($shipping_services_to_hide as & $value) {
            unset($available_shipping_methods[$value]);
        }
    }

    return $available_shipping_methods;
}