Help with calculations based on slicer selection

Check this video for similar solution:

https://www.youtube.com/watch?v=obfYqap4hnQ

Coming back to your .pbix, I quickly fix and it is very slow. You may have to do as per the video or look on internet for better performance.

Optional measure for debug:

Measure debug = var _sv = Max( Prm_Date[Prm_Date] )

RETURN _sv & " : " & 
switch ( _sv, 
  "Date", SELECTEDVALUE(DimDate[Date]),
  "Week", SELECTEDVALUE(DimDate[WeekofYear]),
  "Month", SELECTEDVALUE(DimDate[Month]),
  "Quarter", SELECTEDVALUE(DimDate[Quarter]),
  "Half Year", SELECTEDVALUE(DimDate[Half Year])
  
  , "??")

Actives PW = 
 var _sv = Max( Prm_Date[Prm_Date] )
 RETURN  
CALCULATE(DISTINCTCOUNT('Actives New'[CustomerID])
            ,FILTER(ALL(DimDate), DimDate[Year]=SELECTEDVALUE(DimDate[Year]) &&
                        switch ( _sv, 
                        "Date", DimDate[Date] = SELECTEDVALUE(DimDate[Date]),
                        "Week", DimDate[WeekofYear]=(SELECTEDVALUE(DimDate[WeekofYear])-1) ,
                        "Month", DimDate[Month] = SELECTEDVALUE(DimDate[Month]),
                        "Quarter", DimDate[Quarter] = SELECTEDVALUE(DimDate[Quarter]),
                        "Half Year", DimDate[Half Year]= SELECTEDVALUE(DimDate[Half Year]) 
                        , "??") 
            )
)

Retention % = If ( not ISBLANK([Actives PW]) && [Actives PW] <> 0, 
 ([Active]-[FTD's])/[Actives PW]
)

I just added Measure debug and Actives PW for checking. you can remove those in the below visuals:

sample for half year:

sample for quarter:

Hope it helps!