Dynamic measure dependent on slicer selection

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!