Deliver Message To User If Too Many Items Selected Else Bar Chart

Hi tecumseh ,

Thanks for hnguy71's reply!
If you mean that when the user makes multiple selections, a pop-up warning will appear, or the original bar chart will be changed to a card chart to display information, then I'm sorry that this is not possible in Power BI.
I can give you a workaround:
Here is my sample data:

Use this DAX to create a measure:

Sum of Value = 
VAR _sum =
CALCULATE(
    SUM('Table'[Value]),
    ALL('Table'),
    'Table'[Channel] <= SELECTEDVALUE(Slicer[Channel]) && 'Table'[ID] = MAX('Table'[ID])
)
RETURN
IF(
    COUNTROWS(VALUES(Slicer[Channel])) > 1, 
    BLANK(), 
    _sum
)

Then create the bar chart (column chart):

Use this DAX to create another measure:

ShowMessage = 
IF(
    ISFILTERED(Slicer[Channel]),
    IF(
        COUNTROWS(VALUES(Slicer[Channel])) > 1, 
        "Please select only one channel to view the bar chart.", 
        BLANK()
    ),
    "Please choose one channel"
)

Then create a Card(New) and put the measure into it:

Click Card > Visual > Callout values ​​> Values ​​> enter a space in the field under Show blank as:

Then go to Cards > Background > Change Transparency to 100%:

Also close the Border:

Then overlap the Card (New) and the bar chart:

And the final output is as below:

Best Regards,
Dino Tao
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