You must configure a managed attribute for query refinement.
In the managed attribute's DDR (Dimension Description Record), the mdex-dimension_EnableRefinements attribute must be set to true, so that refinements will be displayed. If the configuration attribute is set to false, refinements will not be displayed (i.e., the managed attribute will be hidden).
If a managed attribute is created and used to classify records, but no records are classified with any corresponding values, that managed attribute will not be available as a refinement, because it is not related to the resulting record set in any way.
No configuration is needed for standard attributes. Assuming that the standard attribute is used to classify records, the corresponding refinement values will be available to create or refine a query.
There are no Dgraph configuration flags necessary to enable the basic displaying of refinements.