adds-gtin-to-product-epxport.php

<?php
/**
 * @snippet       Adds a column for the new GTIN input field on Products so when you export the column shows
 * @author        Serafin Tech
 * @compatible    WooCommerce 9+
 * @website       https://serafintech.io
 */

// Add the GTIN/UPC/EAN/ISBN to the export column names
add_filter('woocommerce_product_export_column_names', 'add_custom_gtin_export_column');
function add_custom_gtin_export_column($columns) {
    // Add a new column for GTIN/UPC/EAN/ISBN
    $columns['global_unique_id'] = 'GTIN/UPC/EAN/ISBN';
    return $columns;
}

// Add the GTIN/UPC/EAN/ISBN data to the export rows
add_filter('woocommerce_product_export_product_row', 'add_custom_gtin_export_row', 10, 3);
function add_custom_gtin_export_row($row, $product, $product_id) {
    // Get the GTIN/UPC/EAN/ISBN value from the product meta
    $gtin_value = get_post_meta($product_id, '_global_unique_id', true);

    // Add the value to the row in the 'global_unique_id' column
    $row['global_unique_id'] = !empty($gtin_value) ? $gtin_value : '';  // Fallback for missing values

    return $row;
}

The new GTIN input field doesn't show in product export. This allows you to export so that the values set in that field show in your export file. Use at your own risk. Tested up to 6.6.2 core and WooCommerce 9.3 Code should be added to your functions.php file of your child theme