How to create Boolean Flag based on selected slicer value ?

cruncher , Try using below steps

Create a new table in Power BI for the parameter selection. This table will have two values: "Current Quarter" and "Previous Quarter".

Add a slicer to your report using the ParameterTable to allow users to select between "Current Quarter" and "Previous Quarter".

Create a measure that calculates the sales based on the selected parameter. This measure will check the selected value and sum the sales accordingly.

SelectedSales =
VAR SelectedParameter = SELECTEDVALUE(ParameterTable[Parameter])
RETURN
SWITCH(
SelectedParameter,
"Current Quarter", CALCULATE(SUM('YourTable'[Sales]), 'YourTable'[Current Quarter Flag] = 1),
"Previous Quarter", CALCULATE(SUM('YourTable'[Sales]), 'YourTable'[Previous Quarter Flag] = 1),

Create a Card Visual:
Add a card visual to your report and set the value to the SelectedSales measure. This will display the total sales based on the selected quarter from the slicer.

Hi cruncher ,

About:

Which approach (SUMX vs Calculate) is more optimized as per your experience if we have 25 Million rows in a table.

For 25 million rows the performance is almost the same.

And here is my sample data:

Here is the parameter table:

You can use this DAX to create a measure:

IsSelectedSource = 
VAR SelectedParam = SELECTEDVALUE(ParameterTable[Source])
RETURN
IF (
    ISFILTERED(ParameterTable[Source]),
    IF(
        MAX('Table'[Source]) = SelectedParam,
        TRUE(),
        FALSE()
    ),
    TRUE()
)

And the final output is as below:

Best Regards,
Dino Tao
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