Show Shipping Method on Invoice? Possible?

You can try this code snippet

/**
 * WP Overnight - PDF Invoices & Packing Slips for WooCommerce
 * Custom function to display the shipping method in the invoice.
 *
 * @param string $document_type
 * @param WC_Abstract_Order $order
 *
 * @return void
 */
function wpo_display_shipping_method( string $document_type, \WC_Abstract_Order $order ): void {
    if ( 'invoice' !== $document_type ) {
       return;
    }

    $document = wcpdf_get_document( $document_type, $order );

    if ( ! empty( $document->get_shipping_method() ) ) {
       echo '<tr class="shipping-method">
          <th>', __( 'Shipping Method:', 'woocommerce-pdf-invoices-packing-slips' ), '</th>
          <td>', $document->shipping_method(), '</td>
       </tr>';
    }
}

add_action( 'wpo_wcpdf_after_order_data', 'wpo_display_shipping_method', 10, 2 );

If you haven’t worked with code snippets (actions/filters) or functions.php before, read this guide: How to use code snippets. We also have a blog post here that you may find helpful about adding custom code to your site.