Using Field Parameters on Columns in matrix

Hi katemarkoska28 

Thank you for reaching out to the Microsoft Fabric Community Forum.
 

Regarding your query on using Field Parameters on columns in a matrix visual, this behavior is due to a known limitation of field parameters  when used in matrix visuals, the selected fields from the parameter tend to display across all column groups, leading to undesired duplication.
 

As a workaround, you can consider creating a custom measure using a SWITCH statement that dynamically returns the appropriate measure based on a selected value from the parameter as suggested by MFelix .

You can then place the Group Label on the matrix columns and use this Matrix Values measure in the Values section of the matrix.
 

Additionally, to improve control over what's displayed, you may also consider using a disconnected slicer table to filter based on the group label (LastMonth, CurrentMonth) and tie it back to your logic using a custom measure as mentioned by DataNinja777 

If this response resolves your query, kindly mark it as Accepted Solution to help other community members. A Kudos is also appreciated if you found the response helpful.
 

Thank You!