WooCommerce: Hide other shipping methods when Free Shipping is available.

function wpexpert28_hide_shipping_when_free_is_available( $rates ) {

    $free_shipping = array();

    // Loop through each shipping rate

    foreach ( $rates as $rate_id => $rate ) {

        // Check if the shipping method is Free Shipping

        if ( 'free_shipping' === $rate->get_method_id() ) {

            $free_shipping[ $rate_id ] = $rate;

        }

    }

    // Return only Free Shipping rates if available, otherwise return all rates

    return ! empty( $free_shipping ) ? $free_shipping : $rates;

}

// Hook into WooCommerce to filter the available shipping rates

add_filter( 'woocommerce_package_rates', 'wpexpert28_hide_shipping_when_free_is_available', 100 );