Suggestions for Measure Optimisation

Hi SpreadsheetNerd  Try this:

WeeksOfSupply =
VAR CurrentSOH = [Closing SOH Quantity]
VAR MaxDate = MAX('Date'[Date])
VAR FutureWeeksTable = CALCULATETABLE(VALUES('Date'[Week Ending]), 'Date'[Date] > MaxDate)
VAR OOSWeek = 
    MINX(
        FILTER(
            FutureWeeksTable,
            CALCULATE(SUM('Date'[Date]), 'Date'[Date] <= EARLIER('Date'[Week Ending])) > CurrentSOH
        ),
        'Date'[Week Ending]
    )
VAR WeeksSupply =
    SWITCH(
        TRUE(),
        ISBLANK(OOSWeek), BLANK(),
        CurrentSOH = BLANK(), BLANK(),
        CurrentSOH < 0, 0,
        NOT(ISBLANK(OOSWeek)),
        VAR FutureDemandExhaustionWeek = 
            CALCULATE(
                [Demand Quantity],
                'Date'[Date] <= OOSWeek,
                'Date'[Date] > MaxDate
            )
        VAR ExcessDemand = FutureDemandExhaustionWeek - CurrentSOH
        VAR DemandInExhaustionWeek = 
            CALCULATE([Demand Quantity], OOSWeek, REMOVEFILTERS('Date'))
        VAR PartDays = DIVIDE(FutureDemandExhaustionWeek - ExcessDemand, DemandInExhaustionWeek)
        RETURN OOSWeek - MaxDate - 1 + PartDays,
        999
    )
RETURN DIVIDE(WeeksSupply, 7, BLANK())

Hope this helps!!

If this solved your problem, please accept it as a solution and a kudos!!

Best Regards,
Shahariar Hafiz