Hi @Anonymous
When you connect to Power BI usage metrics dataset with Power BI Desktop, its connection mode is live connection by default.
Connect to a Power BI service dataset using a live connection
When connect in live connection, it doesn't support get any other dataset in the same pbix. (you will see the modeling is disabled)
Or if you have imported data into a pbix, live connection is disabled because it alreadly contains data from other data sources.
If you import SSAS tabular to Power BI Desktop, to workaround this,
you could connect Power BI usage metrics dataset to power bi desktop,
then add columns from the dataset to a table visual,
next select "..." on the top of the visual and select "export data" to excel or csv file.
finally import this file to the pbix which alreadly contains SSAS tabular data.
Best Regards
Maggie
