Following this answer: https://magento.stackexchange.com/questions/91807/how-to-join-order-grid-collection-to-custom-table-in-magento2/159691 I'm able to join the order custom attribute and show it in the column, the error comes with the filter when applied:

> INNER JOIN `mgnt_sales_order` AS `so` ON main_table.entity_id = so.entity_id WHERE (`custom_attribute` LIKE '%testing the filter%')

> Integrity constraint violation: 1052 Column 'custom_attribute' in where clause is ambiguous

This is because the field is actually in the `sales_order` table and not `sales_order_grid`

*view/adminhtml/ui_component/sales_order_grid.xml*

 <columns name="sales_order_columns">
 <column name="custom_attribute">
 <argument name="data" xsi:type="array">
 <item name="config" xsi:type="array">
 <item name="visible" xsi:type="boolean">true</item>
 <item name="filter" xsi:type="string">text</item>
 <item name="label" xsi:type="string" translate="true">Custom Attribute</item>
 </item>
 </argument>
 </column>
 </columns>

*Plugins/AddColumnsSalesOrderGridCollection.php*

 <?php namespace Vendor\Module\Plugins;
 
 use Magento\Framework\Message\ManagerInterface as MessageManager;
 use Magento\Sales\Model\ResourceModel\Order\Grid\Collection as SalesOrderGridCollection;
 
 class AddColumnsSalesOrderGridCollection
 {
 private $messageManager;
 private $collection;
 
 public function __construct(MessageManager $messageManager,
 SalesOrderGridCollection $collection
 ) {
 
 $this->messageManager = $messageManager;
 $this->collection = $collection;
 }
 
 public function aroundGetReport(
 \Magento\Framework\View\Element\UiComponent\DataProvider\CollectionFactory $subject,
 \Closure $proceed,
 $requestName
 ) {
 $result = $proceed($requestName);
 
 $tableSalesOrder = $this->collection->getResource()->getTable('sales_order');
 
 if ($requestName == 'sales_order_grid_data_source') {
 if ($result instanceof $this->collection) 
 {
 $select = $this->collection->getSelect();
 
 $select->join(
 ["so" => $tableSalesOrder],
 'main_table.entity_id = so.entity_id',
 array('so.custom_attribute')
 )
 ->distinct();
 }
 
 }
 return $this->collection;
 }
 }

**Goal:** Filter the orders grid by a custom attribute of the order.

Unfortunally the solution with the plugin above creates other problems in the order view.. that's why I'm looking for other solutions