Power Query - Recursive decomposition of rows

Hello Ira_27,

Can you please try this approach:

1. Create a Recursive Table

DecomposedHoldings = 
VAR FundHoldings = 
    GENERATE(
        'Holdings',
        FILTER(
            'Holdings',
            'Holdings'[FundID] = EARLIER('Holdings'[AccountID])
        )
    )
RETURN
    UNION('Holdings', FundHoldings)

2. Calculate % Investment

% Investment = 
VAR TotalMV =
    CALCULATE(
        SUM('DecomposedHoldings'[MV]),
        ALL('DecomposedHoldings')
    )
RETURN
    DIVIDE(SUM('DecomposedHoldings'[MV]), TotalMV, 0)

3. If the semantic model's size is an issue, filter the data in Power Query:

FilteredHoldings = Table.SelectRows(
    Source,
    each [HoldingDate] >= Date.AddMonths(DateTime.LocalNow(), -24)
)

Hope this helps!