WooCommerce Exclude Free Shipping

functions.php

<?php
function free_shipping_based_on_cart_shipping_class( $is_available ) {

	$cart_items = WC()->cart->get_cart();
	
	foreach ( $cart_items as $cart_item ) {

		$product = $cart_item['data'];
		$class   = $product->get_shipping_class();
		
		// start slugs of shipping classes excluded from free shipping with 'bulk'
		if ( substr($class, 0, 4) === 'bulk' ) {
			return false;
		}
	}
	
	return $is_available;
}
add_filter( 'woocommerce_shipping_free_shipping_is_available', 'free_shipping_based_on_cart_shipping_class' );