Slicer affecting measure

Hi

I am trying to count the total number of people that joined the business in the last two years.

I want to be able to use a slicer to select the current reporting period and then return all the new joiners from the 1st of January from 2 years before the last date of the selected period. 

So selecting any period that ends in 2023 would return all the joiners since 01/01/2021, a period ending in 2024 will return all joiners since 01/01/2022 and so on.

TotalNotMaleJoiners (Heads) L2Y = 
    CALCULATE(
        [TotalJoiners (Heads)]
        ,FILTER(
            'PersonDim',
            'PersonDim'[Gender] <> "Male"
        )
        ,FILTER(
            'DateDim',
            'DateDim'[FullDate] IN

            VAR SelectedYear = 
            YEAR(
                MAXX(
                    ALL('DateDim'),
                    SELECTEDVALUE('DateDim'[FullDate], TODAY()
                    )
                )
            )

            VAR Jan1TwoYearsAgo = 
            DATE(SelectedYear - 2,1,1)

            VAR PeriodMaxDate =             
            MAXX(
                ALL('DateDim'),
                SELECTEDVALUE('DateDim'[FullDate], TODAY()
                )
            )

            RETURN
            DATESBETWEEN('DateDim'[FullDate],Jan1TwoYearsAgo,PeriodMaxDate)
        )
    )

When I use a slicer to select a period it is overwriding all the date min/max, I'm assuming I need to wrap something with an ALL/ALLSELECTED but I've tried it all over the place and whatever I do the slicer seems to affect the measure.

Any help greatly appreciated.

My slicer is from a column in the DateDim table but is a text value so I can't just use MAX or MAXX on that.