When looping through the items in an order pass the $item to this function to get the quantity returned from the line item.

WooCommerce: Get Returned Count from Line Item in Order

function zf_get_line_item_returned_quantity( $item, $order ) {
    
    $returned_quantity = 0;

    foreach ($order->get_refunds() as $refund) {
        foreach ($refund->get_items() as $refund_item) {
            if ($refund_item->get_product_id() == $item->get_product_id()) {
                $returned_quantity += $refund_item->get_quantity();
            }
        }
    }

    return $returned_quantity;
	
}