Power BI - Dynamic measure based on slicer selection

Question

I have read several articles about that but nothing really helped me so I hope that anyone can help me here. I have the following measure:

M_Act_FTE_monthly = 
IF(
    ISFILTERED('summary_report'[Time Period]);
    ERROR("Time intelligence quick measures can only be grouped or filtered by the Power BI-provided date hierarchy or primary date column.");
    TOTALMTD(
        SUM('summary_report'[Act_FTE]);
        'summary_report'[Time Period].[Date]
    )
)

This one works for all of my ProjTypes. Now, I want to implement this measure for the ProjTypes I selected in the Slicer. This is my slicer:

Do you have any ideas how to dynamically change the measure above? Any help is appreciated!