Reply To: Ordering/Grouping Out of Stock Items to the bottom of the search results

In that case, you can still try the group priorities feature. Try creating a rul group and set the priority to 101. Then the rule should be on the “_stock_status” custom field: https://i.imgur.com/Qo7Tqmb.png
After saving the groups, the items in stock should be prioritized, and the primary/secondary ordering applied by group basis.

To make direct changes to the final query, you can use these hooks.