Slow cumulative running total

To have the best of time intelligence prefer to have Date Dimension. Try formula like

Running Total = CALCULATE(
    SUM('Table_1'[SUM1]),
    FILTER(
        ALL('Date'),'Date'[Date]<= MAX('Date'[Date])
    )
)
Running Total = CALCULATE(
    SUM('Table_1'[SUM1]),
    FILTER(
        ALLSELECTED('Date'[Date]),ISONORAFTER('Date'[Date], MAX('Date'[Date]), DESC)
    )
)

To get the best of the time intelligence function. Make sure you have a date calendar and it has been marked as the date in model view. Also, join it with the date column of your fact/s. Refer :
https://radacad.com/creating-calendar-table-in-power-bi-using-dax-functions
https://www.archerpoint.com/blog/Posts/creating-date-table-power-bi
https://www.sqlbi.com/articles/creating-a-simple-date-table-in-dax/

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Thanks. My Recent Blogs -Decoding Direct Query - Time Intelligence, Winner Coloring on MAP, HR Analytics, Power BI Working with Non-Standard TimeAnd Comparing Data Across Date Ranges
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