Three measures are used:

   Check Filtered =
    IF (

        ISFILTERED ( Organisations[Organisation/Forums/Treaties] ),
        1,
        0
   )

   Card Message =
    IF (
         ISFILTERED ( Organisations[Organisation/Forums/Treaties] ),
         “”,
          “You must select an organisation to know full details”
   )

   Make Transparent =
      IF (     
           ISFILTERED ( Organisations[Organisation/Forums/Treaties] ),
          “#FFFFFF00”,
          “White”
   )

  Show or Hide a Power BI Visual Based on Selection

• Create a card to work as a mask for the visual.

• Write a measure to display a user message on the card based on the user selection (type Text).

• Write a measure to render the visual blank when nothing is selected.

• Write a measure that returns either the background colour or “transparent” based on the user selection, and set that to conditionally format the background colour of the card.