This code will send an email to the WooCommerce store owner for Pending Payment orders

wc-store-onwer-pending-payment-email.php

// New order notification only for "Pending" Order status
add_action( 'woocommerce_checkout_order_processed', 'pending_new_order_notification', 20, 1 );
function pending_new_order_notification( $order_id ) {
    // Get an instance of the WC_Order object
    $order = wc_get_order( $order_id );

    // Only for "pending" order status
    if( ! $order->has_status( 'pending' ) ) return;

    // Get an instance of the WC_Email_New_Order object
    $wc_email = WC()->mailer()->get_emails()['WC_Email_New_Order'];

    ## -- Customizing Heading, subject (and optionally add recipients)  -- ##
    // Change Subject
    $wc_email->settings['subject'] = __('{site_title} - New customer Pending order ({order_number}) - {order_date}');

    // Change Heading
    $wc_email->settings['heading'] = __('New customer Pending Order'); 
    // $wc_email->settings['recipient'] .= ',name@email.com'; // Add email recipients (coma separated)

    // Send "New Email" notification (to admin)
    $wc_email->trigger( $order_id );
}

Thanks @stuartduff !