Attached to the PowerBI datasource is a method called ExecuteDatasetQuery that appears to be for submitting DAX queries to a PBI dataset. I've burned an entire day trying to understand how this thing is supposed to work and your documentation is... lacking. At any rate, I can't get a single query (that otherwise functions everywhere else DAX queries can be executed) to return something meaningful within PowerApps.
Any query, even something as simple as
EVALUATE(MyTable)
returns the following:

I can CountRows on the result of running
ClearCollect(_result,PowerBI.ExecuteDatasetQuery(workspaceGUID,datasetGUID,queryString));
and see exactly the number of rows I'd expect to see when running this query anywhere else, but the collection itself has no columns and now values.
Any help?
P.S., I'd love to do this in Power Automate, since that's a much nicer way to set these things up but y'all don't appear super invested in making that useful so...