Dynamic formula that splits/distributes revenue a value among various monthly start and end dates

PeterBartholomew1  I am looking for some help to create the excel formulas (If and AND /OR ) Functions for the following dependent on the "Treatment" Column. If Spread evenly, then cost should split evenly over the start and end date. If End of Quarter, then should be adjusted accordingly  and so on. Can you help?

John_Bloggs650 

The formula used functionality that is only available in 365 and started rollout around the beginning of 2019.  A starting point would be the Microsoft blog posts on Dynamic Arrays, Lambda Functions and Lambda helper functions.  The last thing to appear was the array shaping functions such as VSTACK. 

Excel Dynamic Array Improvements (microsoft.com)

John_Bloggs650 

The function was extracted from a workbook that used a month-based timeline with period start and period end dates (the 1st and 28/29/30/31st respectively).  It could be that would be more use to you.

Some functions:

Addλ = LAMBDA(x, y, x + y);

Timelineλ = LAMBDA(modelStart, duration, [option],
    LET(
        numberPeriods,  duration*MPY,
        counter,        SEQUENCE( , numberPeriods),
        periodEnds,     EOMONTH(modelStart, counter-1),
        periodStarts,   1 + EOMONTH(periodEnds, -1),
        SWITCH(option, 0, periodStarts, 1, periodEnds, counter)
    ));

UniformSpreadλ = LAMBDA(amount, eventStart, [duration],
    LET(
        months, IF(ISOMITTED(duration),1,duration),
        eventFinish,    EOMONTH(eventStart, months - 1),
        withinPeriod,  (modelPeriodBegins# >= eventStart) * 
                       (modelPeriodEnd#    <= eventFinish),
        IF(withinPeriod, amount/months, 0)
    )
);

SeasonallyAdjustedλ = LAMBDA(base, adjustment,
    LET(
      appliedSeasonalityAdj, INDEX(adjustment, MONTH(modelPeriodBegins#)),
      appliedSeasonalityAdj * base
   ));

StepIncreaseλ = LAMBDA(base, ratio, eventStart,
    IF(modelPeriodBegins#<eventStart, base, base*ratio)
);

The book also had a function to accumulate a balance from inflows and outflows and apply interest payment on positive balances but that is well out of scope here.

John_Bloggs650 

Since your examples show days, I adapted a Lambda function to work with days.  I would always introduce a Lambda function in modelling situations where assumption data needs to be converted to a time series because it hides irrelevant detail.

UniformSpreadλ = LAMBDA(amount, eventStart, [duration],
    LET(
        days, IF(ISOMITTED(duration), 1, duration),
        eventFinish, eventStart + days - 1,
        withinPeriod, (modelPeriod# >= eventStart) *
            (modelPeriod# <= eventFinish),
        IF(withinPeriod, amount / days, 0)
    )
);

Not that the function is set to accept a duration rather than an end date but the two options are equivalent.