drillthrough-button not activated in drill down

Hii jonas_poskowsky 

You're right  SELECTEDVALUE(), ISFILTERED() and HASONEVALUE() all return values during drill-down, but Power BI still does not treat that as a true data-point selection. Drill-down only changes filter context; it does not create a “point selection event”, and the drill-through button activates only when a data point is explicitly clicked at the lowest level. This internal selection state is not exposed in DAX, so there is no function that allows us to distinguish “drill-down context” vs “actual point selection”. That’s why the button can detect the difference, but your custom measure cannot  it’s a limitation of the visual interaction model, not your DAX.