DAX Boolean Calculation

This might work. I returned 1 or 0. I would not return TRUE or FALSE. You can return those text values, but I would shy away from returning a true boolean value in DAX. It can cause issues with getting some code to work. I always convert to 1/0 or text values "T" or "F" or whatever you want.

Some Column =
IF(
    table1.[column1] = "A",
    IF(
        RELATED( table2.[date] ) >= table1.[startdate]
            && RELATED( table2.[date] )
                <= RELATED( table2.[enddate] ),
        1,
        0
    ),
    IF(
        table1.[column1] = "B",
        IF(
            RELATED( table2.[date] ) >= table1.[startdate]
                && RELATED( table2.[date] )
                    <= RELATED( table2.[endate] ),
            1,
            0
        )
    )
)

It is also only going to work if the tables are related through a common dimension table, and even then, this is something that is best done in Power Query or the data source via a merge with a comparison. Cannot say for sure as you included no data.

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