DAX code
Slicer Selection Count =
COUNTROWS(VALUES('Product'[ProductName]))
Counts how many distinct values are currently selected on a slicer.
Type your table and column names once. Every measure below updates.
Slicer Selection Count =
COUNTROWS(VALUES('Product'[ProductName]))
Replace 'Product'[ProductName] with the column bound to the slicer you want to count selections for.
Browse all 175 measures in the Power BI DAX Measures Library, or search the library for something similar to Slicer Selection Count.