dynamic diff calculation row in matrix

Dear Power BI Gurus !

I'm struggling for some time already with creating of dynamic calculation which would return difference between selected rows in matrix. Here's a sample of raw data:

Then, matrix should enable to select Foorecast ID in slicer while the calculation row should indicate a diff (Forecast variance) between last and previous forecast:

I tried to use measures for each Forecast ID and it worked. It calculates the diff but if I select two particular Forecast IDs I get all measures rows visible in matrix (selected ones are with values and not selected ones with empty cells). What I need is to visualize only selected Forecast IDS and Forecast variance row at the end.

Do You have a smart solution for it ?

I'd appreciate Your support.

Have a great day !