Hide all paid shipping methods in WooCommerce when free shipping is available. Just drop this code in your functions.php or custom plugin and you're good to go! Perfect for stores that want to encourage free shipping usage.

woocommerce-display-only-free-shipping-method-when-available.php

<?php
add_filter('woocommerce_package_rates', 'hide_shipping_when_free_is_available', 100);

function hide_shipping_when_free_is_available($rates) {
    $free = array();
    
    // Find free shipping methods
    foreach ($rates as $rate_id => $rate) {
        if ('free_shipping' === $rate->method_id) {
            $free[$rate_id] = $rate;
            break;
        }
    }
    
    // If free shipping is available, return only free shipping options
    if (!empty($free)) {
        return $free;
    }
    
    return $rates;
}