Group top 20 customers

Hi,

I am not sure how your semantic model looks like, but I tried to create a sample pbix file like below.

In my sample, I described top 5 but I hope you can make it to show top 20 in your sample.

Please check the below picture and the attached pbix file.

WINDOW function (DAX) - DAX | Microsoft Learn

Top 5 and others: =
VAR _topN = 5
VAR _topNlist =
    WINDOW (
        1,
        ABS,
        _topN,
        ABS,
        ALL ( customer[customer] ),
        ORDERBY ( CALCULATE ( SUM ( sales[sales] ) ), DESC )
    )
VAR _topNsales =
    CALCULATE ( SUM ( sales[sales] ), _topNlist )
VAR _topNsaleskeepfilter =
    CALCULATE ( SUM ( sales[sales] ), KEEPFILTERS ( _topNlist ) )
VAR _allsales =
    CALCULATE ( SUM ( sales[sales] ), REMOVEFILTERS ( customer[customer] ) )
VAR _othersales = _allsales - _topNsales
RETURN
    SWITCH (
        TRUE (),
        SELECTEDVALUE ( category[category] ) = "others", IF ( NOT HASONEVALUE ( customer[customer] ), _othersales ),
        SELECTEDVALUE ( category[category] ) = "top_N", _topNsaleskeepfilter,
        _allsales
    )