How to plot maximum/minimum value plot for selected item's category

Try the following change:

Maximum =
VAR CategorySelection =
    VALUES( TableDimension[Category] )
RETURN
    CALCULATE (
        MAX ( Table[Sales] ),
        FILTER ( ALL ( TableDimension ), TableDimension[Category] in CategorySelection )
    )

Hi Maggi029 ,

Try to change the metric of the max/min to somwething similar to this:

Maximum =
VAR CategorySelection =
    VALUES( TableDimension[Category] )

var ItemValues =   CALCULATE (
        DISTINCTCOUNT ( Table[Item] ),
        FILTER ( ALL ( TableDimension ), TableDimension[Category] in CategorySelection )
    )

RETURN
IF(ItemValues > 1,
    CALCULATE (
        MAX ( Table[Sales] ),
        FILTER ( ALL ( TableDimension ), TableDimension[Category] in CategorySelection )
    )
)

This should return blank for the maximum and minimum when there is only a single value so the labels will not appear.