This tutorial explains the dropdown slicer. Have fun discovering ways to format slicer as a dropdown list.
First of all enter some ad-hoc data, select Enter Data icon
Then put arbitrary data in the table:
Click load to load the data to the Power BI desktop. When you select Load, Power BI Desktop creates a new table from your data and makes it available in the Fields pane.
On the Overview page, with nothing selected on the canvas, select the Slicer icon slicer icon in the Visualizations pane to create a new slicer.
With the new slicer selected, from the Fields pane, select Countries > Country to populate the slicer. The new slicer is a list with selection boxes before the names.
Now, go back to your slicer and hover over this spot right here…
Choose “Dropdown”. Now you should have this:
And then You have turned your slicer into a drop-down list.