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Hi  dommyw277 ,

I created some data:

Here are the steps you can follow：

1. Create measure.

Count =
var _select=SELECTEDVALUE('Table'[Month])
return
COUNTX(FILTER(ALL('Table'),'Table'[Month]=_select&&'Table'[Group]=MAX('Table'[Group])),[Group])

rank =
RANKX(ALL('Table'),[Count],,DESC,Dense)

Flag =
IF(
    [rank]<=10,1,0)

2. Place [Flag]in Filters, set is=1, apply filter.

3. Result:

For errors, you can refer to:

https://community.powerbi.com/t5/Desktop/Column-cannot-be-found-or-may-not-be-used-in-this-expression/m-p/84327

If I have misunderstood your meaning, please provide your desired output and your pbix without privacy information.

If you need pbix, please click here.

Best Regards,

Liu Yang

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