You need help writing DAX.

Anonymous 

See if this works for you (apologies since I din't apply the colour coding you have in your original):

1) To calculate the new clients by month:

New clients in month =
VAR PrevYM =
     ( MAX ( FactDigitalStrategy[Year] ) - 1 ) * 100
        + RIGHT ( SELECTEDVALUE ( FactDigitalStrategy[MonthYearNo] ), 2 )
VAR ActualClients =
    VALUES ( FactDigitalStrategy[ClientKey] )
VAR PrevYearMonthClients =
    CALCULATETABLE (
        VALUES ( FactDigitalStrategy[ClientKey] ),
        FILTER (
            ALL ( FactDigitalStrategy ),
            FactDigitalStrategy[MonthYearNo] = PrevYM
        )
    )
RETURN
    COUNTROWS ( EXCEPT ( ActualClients, PrevYearMonthClients ) )

2) To filter the visuals based on the selection in the slicers, I created a new disconnected table for the new and active clients (and used this table for the visuals)

3) To filter the visuals, I created a measure to use in the filters for the visuals in the filter pane:

New client table (Filtered) =
IF (
    SELECTEDVALUE ( '1 New client table'[MonthYearNbr] )
        <= SELECTEDVALUE ( DimDate[MonthYearNbr] ),
    1
)

Let us know if you need further help

I'm attachiing the sample PBIX file