Improve Measure Performance with nested IF(CALCULATE()

I'm gussing becasue of the auto date time table behind the [Phase Since Date] . Better if you had a proper date table or a simple coulmn for the quarter like you have for the [DME Handover Quarter] column

Again, without looking at your model, I'm actually gussing by your code how it looks like ‌‌ so try this:

Contrib FlexQ SUMMARY =
VAR selectperiod =
    SELECTEDVALUE ( '** Period Create'[Period] )
VAR selectcontrib =
    SELECTEDVALUE ( '** Contributor'[Contrib] )
VAR periodq =
    VALUE ( MID ( selectperiod, 2, 1 ) )
VAR Q1_DME =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
		KEEPFILTERS('CX Cloud Pipeline'[DME Handover Quarter] = "2022-Q1")
    )
VAR Q2_DME =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
        KEEPFILTERS(
        	FILTER(
        		SUMMARIZE(
        			ALL('CX Cloud Pipeline'),
	        		'CX Cloud Pipeline'[DME Handover Quarter],
	        		'CX Cloud Pipeline'[Phase Since Date].[QuarterNo],
	        		'CX Cloud Pipeline'[Phase Since Date].[Year]
	        	),
	            'CX Cloud Pipeline'[DME Handover Quarter] = BLANK ()
	                && 'CX Cloud Pipeline'[Phase Since Date].[QuarterNo] = 2
	                && 'CX Cloud Pipeline'[Phase Since Date].[Year] = 2022
	           )
        )
    )
VAR FY_DME =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
        KEEPFILTERS(
        	FILTER(
        		SUMMARIZE(
        			ALL('CX Cloud Pipeline'),
	        		'CX Cloud Pipeline'[DME Handover Quarter],
	        		'CX Cloud Pipeline'[Phase Since Date].[QuarterNo],
	        		'CX Cloud Pipeline'[Phase Since Date].[Year]
	        	),
            'CX Cloud Pipeline'[DME Handover Quarter] = "2022-Q1"
                || ( 'CX Cloud Pipeline'[Phase Since Date].[QuarterNo] = 2
                && 'CX Cloud Pipeline'[Phase Since Date].[Year] = 2022 )
        	)
        )
    )
VAR Q1 =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
		KEEPFILTERS('CX Cloud Pipeline'[Creation Quarter] = "2022-Q1")
    )
VAR Q2 =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
		KEEPFILTERS('CX Cloud Pipeline'[Creation Quarter] = "2022-Q2")
    )
VAR FY =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
        KEEPFILTERS('CX Cloud Pipeline'[Creation Year] = 2022 )
    )
VAR R4Q =
    CALCULATE (
        SUM ( 'CX Cloud Pipeline'[acv €] ),
			KEEPFILTERS('CX Cloud Pipeline'[Closing Quarter] IN { "2022-Q2", "2022-Q3", "2022-Q4", "2023-Q1"} ))
RETURN
    SWITCH (
        TRUE (),
        selectperiod = "R4Q", R4Q,
        selectperiod = "Q122"
            && selectcontrib = "DME", Q1_DME,
        selectperiod = "Q222"
            && selectcontrib = "DME", Q2_DME,
        selectperiod = "FY22"
            && selectcontrib = "DME", FY_DME,
        selectperiod = "Q122"
            && selectcontrib <> "DME", Q1,
        selectperiod = "Q222"
            && selectcontrib <> "DME", Q2,
        selectperiod = "FY22"
            && selectcontrib <> "DME", FY
    )