hide most expensive shipping method

Here is my snippet, feel free to modify as you need.

function hide_flat_rate_if_free_shipping_available($rates) {
    $free_shipping = false;
    $flat_rate = false;

    // Check available methods
    foreach ($rates as $rate_id => $rate) {
        if ('free_shipping' === $rate->method_id) {
            $free_shipping = true;
        }
        if ('flat_rate' === $rate->method_id) {
            $flat_rate = $rate_id;
        }
    }

    // If both methods are available, remove flat rate shipping and keep free shipping
    if ($free_shipping && $flat_rate) {
        unset($rates[$flat_rate]);
    }

    return $rates;
}
add_filter('woocommerce_package_rates', 'hide_flat_rate_if_free_shipping_available', 100);