The VisibleProducts variable contains a list of products for the selection currently displayed in the visual. In the example, we have the top 3 products for each Product Category included in our report. The ranking that is returned is only up to the value selected in the TopN parameter – for this reason, we can use the result of Ranking by Sales to filter the visual, including only the products ranked in the 1-to-TopN Value range. We use a filter in the Power BI filter pane to accomplish this task.
This is a common enough pattern that I do wish Power BI made it easy.