WooCommerce - How to check for Guest Orders

functions.php

//set the email address
$email = 'your@ema.il';

//get orders using the customer email address
$query = new WC_Order_Query();
$query->set( 'customer', $email );
$query->set( 'limit', -1 );
$orders = $query->get_orders();

//check if not a WordPress user but orders do exist
$wp_user = get_user_by( 'email', $email );
$guest_orders = [];
if( empty( $wp_user ) && ! empty( $orders ) ){
  //we are a guest user
    foreach ( $orders as $order ) {
        $status = $order->get_status();
        if ( $status = 'completed' ) {
            $guest_orders[] = [$order->get_id() => $order->get_status()];
        }
    }
}

//let's see the results
print_r( $guest_orders );