To compute the percentage of total sales per region while dynamically adjusting to filters, use this DAX measure:
RegionalSalesPercentage = 
DIVIDE(
    SUM(Sales[SalesAmount]), 
    CALCULATE(SUM(Sales[SalesAmount]), ALLSELECTED(Sales))
)
Explanation:
- SUM(Sales[SalesAmount]) calculates the total sales for the current region.
 
- CALCULATE(..., ALLSELECTED(Sales)) ensures the denominator reflects the filtered total sales based on slicers.
 
- DIVIDE prevents division errors if the total sales are zero.