Grouping by a column while doing the calculation inside the DAX.

To apply your calculation grouped by HsCode, you’ll need to wrap your calculation in SUMX over a grouped table, so each group (by HsCode) calculates independently and then aggregates.

Modified DAX with Grouping by HsCode:

MSR_CBAM_Value_Certificate_Cost_All_Actual =
VAR SelectedThresholdType = SELECTEDVALUE('Threshold Unit'[Threshold Unit])
RETURN
SUMX(
    VALUES(CBAM_Value_Volume_Summary[HsCode]),
    VAR CurrentHsCode = CBAM_Value_Volume_Summary[HsCode]
    RETURN
        CALCULATE(
            (
                (
                    SUM ( CBAM_Value_Volume_Summary[Annex_I_Default_specific_embedded_emissions] )
                        - (
                            SUM ( CBAM_Value_Volume_Summary[CBAM_Benchmark] )
                                * ( MAX ( CBAM_Value_Volume_Summary[FactorPercentage] ) / 100 )
                        )
                )
                * ( SUM ( CBAM_Value_Volume_Summary[ImportVolume] ) * MAX ( CBAM_Value_Volume_Summary[Annual_Factor] ) )
            )
            * [MSR_CBAM_Threshold_Value_Price_Actual],
            FILTER (
                CBAM_Value_Volume_Summary,
                CBAM_Value_Volume_Summary[HsCode] = CurrentHsCode &&
                CBAM_Value_Volume_Summary[TotalCustomsValue] > [MSR_CBAM_Threshold_Value_Price_Actual] &&
                CBAM_Value_Volume_Summary[ThresholdType] = SelectedThresholdType &&
                CBAM_Value_Volume_Summary[Year] = MAX(CBAM_Value_Volume_Summary[Year])
            )
        )
)