Hey @CodeGoblin ,
To my knowledge the query param doesn’t work to filter products within a collection at all, so there wouldn’t be a day to do this I’m afraid. This is done because the queries that need to be performed to filter that way can be extremely expensive, so for performance reasons we don’t allow it.
If you needed to filter based on inventory I think the way you had been doing it with the products root query is the way to go. Or, alternatively, you could still query products within a collection, and then add ‘totalInventory’ as a return value of the products and then filter ones that are out of stock manually.