I tried in many ways to filter out specific orders from WooCommerce that contain relevant simple & variable products (with ACF information) and then export them via XML to my fulfillment partner.

For that, I am using WP ALL EXPORT PRO and ACF plugins with a custom code:

USED IN XML EDITOR of WP ALL EXPORT PLUGIN

<?xml version="1.0" encoding="UTF-8"?>
<orders>
    <!-- BEGIN LOOP -->
    <order>
        <commission>{Bestell ID}</commission>
        <production>2</production>

        <receiver>
            <line1>{Shipping First Name} {Shipping Last Name}</line1>
            <line2>{Shipping Company}</line2>
            <street>{Shipping Address 1}</street>
            <streetnumber>{Shipping Address 2}</streetnumber>
            <country_code>{Shipping Country}</country_code>
            <zip>{Shipping Postcode}</zip>
            <city>{Shipping City}</city>
            <email>{Customer Account Email Address}</email>

        </receiver> 

        <items> 
            [my_get_order_items({Bestell ID})]
        </items>
    </order>
    <!-- END LOOP -->
</orders>

USED IN FUNCTION PHP EDITOR OF WP ALL EXPORT PLUGIN

function my_get_order_items($Bestell_id) {
    // Check if the Bestell ID is valid
    if (!$Bestell_id) {
        return false;
    }
    
    // Fetch the order
    $order = wc_get_order($Bestell_id);
    if (!$order) {
        return false;
    }

    // Initialize the string to store order details
    $order_details = "";

    // Loop through each order item
    foreach ($order->get_items() as $item_id => $item) {
        // Get the product object
        $product = $item->get_product();

        // Skip if there's no product associated with the item
        if (!$product) 
        { continue; }
        
        
        if (!(
strpos($item->get_name(), 'KERAMIKTASSE') !== false ||
strpos($item->get_name(), 'BAUMWOLLTASCHE') !== false ||
strpos($item->get_name(), 'T-SHIRT') !== false))
{ continue; }
        
        $order_details .= "**LT**item**GT**";
        $order_details .= "**LT**ID**GT**" . $product->get_sku() . "**LT**/ID**GT**";
        $order_details .= "**LT**produktname**GT**" . $item->get_name() . "**LT**/produktname**GT**";
        $order_details .= "**LT**amount**GT**" . $item->get_quantity() . "**LT**/amount**GT**";
        $order_details .= "**LT**upload**GT**" . maybe_serialize( get_field( 'upload', $product->get_id() ) ) . "**LT**/upload**GT**";
        $order_details .= "**LT**size**GT**" . maybe_serialize( get_field( 'size', $product->get_id() ) ) . "**LT**/size**GT**";
        $order_details .= "**LT**groesse**GT**" . maybe_serialize( get_field( 'produktgröße', $product->get_id() ) )  . "**LT**/groesse**GT**";
        $order_details .= "**LT**material**GT**" . maybe_serialize( get_field( 'material', $product->get_id() ) ) . "**LT**/material**GT**";
        $order_details .= "**LT**print**GT**" . maybe_serialize( get_field( 'print', $product->get_id() ) ) . "**LT**/print**GT**";
        $order_details .= "**LT**variante**GT**" . maybe_serialize( get_field( 'variante', $product->get_id() ) ) . "**LT**/variante**GT**";
        $order_details .= "**LT**category**GT**" . maybe_serialize( get_field( 'category', $product->get_id() ) ) . "**LT**/category**GT**";
        
        //add options to the output
        $order_details .= "**LT**Options**GT**";
            $order_details .= "**LT**Option**GT****LT**ID**GT**" . "1996" . "**LT**/ID**GT****LT**Value**GT**" . maybe_serialize( get_field( 'value_115', $product->get_id() ) ) . "**LT**/Value**GT****LT**/Option**GT**";
        
            $order_details .= "**LT**Option**GT****LT**ID**GT**" . "2489" . "**LT**/ID**GT****LT**Value**GT**" . maybe_serialize( get_field( 'value_117', $product->get_id() ) ) . "**LT**/Value**GT****LT**/Option**GT**";
        
            $order_details .= "**LT**Option**GT****LT**ID**GT**" . "2056" . "**LT**/ID**GT****LT**Value**GT**" . maybe_serialize( get_field( 'value_118', $product->get_id() ) ) . "**LT**/Value**GT****LT**/Option**GT**";
        
        $order_details .= "**LT**/Options**GT**";
        
        $order_details .= "**LT**/item**GT**";
        
    }

    return $order_details;
}

This code works well so far and all relevant orders and all relevant products are filtered. The only problem I have is that only the ACF field information for simple products is exported. For variable products all ACF fields remain empty.

How I can finally transfer variable products + ordered product variants via xml – analogue to “simple products”?

How do I have to change my PHP code and/or ACF settings?