Need help with Measure for Matrix Table and Top 5

Ok, I've been playing around with the clustered column chart and this is what I have so far:

Change the [Sort measure] to:

Sort measure =
VAR _FreqByCity =
    CALCULATE (
        [Count Frequency],
        FILTER (
            ALL ( InjuryCause[Cause Grouping] ),
            [Top 5 by frequency and Incurred] < 6
        )
    )
VAR _LN =
    LEN (
        FORMAT (
            CALCULATE (
                [Count Frequency],
                ALL ( 'LossRunToExcel'[Reporting Location City] )
            ),
            "text"
        )
    )
VAR _Pre =
    _FreqByCity
        * POWER ( 10, _LN * 2 )
VAR _Inc =
    CALCULATE (
        RANKX (
            ALLSELECTED ( LossRunToExcel[Reporting Location City] ),
            [Sum of Total Gross Incurred],
            ,
            ASC,
            DENSE
        ),
        ALLSELECTED ( InjuryCause[Cause Grouping] )
    )
VAR _Mid =
    _Inc * POWER ( 10, _LN )
RETURN
    IF (
        ISBLANK ( [Count Frequency] ),
        BLANK (),
        _Pre + _Mid
            + RANKX ( ALLSELECTED ( InjuryCause[Cause Grouping] ), [Ref],, ASC, SKIP )
    )

If you now create the clustered column chart with the default options, adding filters to the filter pane to limit the cities, you can get what you are looking for, albeit it isn't particularly pretty:

 If you prefer, you can create a more appealing visual as follows (albeit it might require maintenance, because we need to create a separate table for the legend colours which means if the dataset grows in cause groupings, you will need to update the legend table accordingly)

I've created the legend colour code using DAX as follows:

Legend colour code =
ADDCOLUMNS (
    SELECTCOLUMNS (
        DISTINCT ( InjuryCause[Cause Grouping] ),
        "Lengend Case Grouping", InjuryCause[Cause Grouping],
        "Index",
            RANKX (
                VALUES ( InjuryCause[Cause Grouping] ),
                InjuryCause[Cause Grouping],
                ,
                ASC
            )
    ),
    "Colour Code",
        SWITCH (
            [Index],
            1, "#0065A2",
            2, "#99E3F8",
            3, "#F98A3C",
            4, "#605F61",
            5, "#379810",
            6, "#C635A7",
            7, "#B90000",
            8, "#004B82",
            9, "#03B1E4",
            10, "#DFBFBF",
            11, "#9C4102",
            12, "#5F6B6D",
            13, "#FB8281",
            14, "#D4F6C6",
            15, "#4B3FF0",
            16, "#A4DDEE",
            17, "#B69ECD",
            18, "#B687AC",
            19, "#28738A",
            20, "#E6E6E6",
            21, "#168980",
            22, "#293537",
            23, "#BB4A4A",
            24, "#F2F549",
            25, "#939600"
        )
)

So the problem with this method is that if new "Case groupings" appear, you need to update and add new colour codes in the switch function.

The model is now as follows:

You can now create the same column chart as the default, but leave out the legend. You can use the following measure for the conditional formatting of the columns:

Colour legend =
LOOKUPVALUE (
    'Legend colour code'[Colour Code],
    'Legend colour code'[Lengend Case Grouping], MAX ( InjuryCause[Cause Grouping] )
)

Create a separate legend using a matrix visual as follows (you will need this measure to filter the values in the legend):

Filter Legend =
VAR _Table =
    ADDCOLUMNS (
        SUMMARIZE (
            LossRunToExcel,
            LossRunToExcel[Reporting Location City],
            'InjuryCause'[Cause Grouping]
        ),
        "@Rows",
            IF (
                CALCULATE (
                    RANKX (
                        ALL ( LossRunToExcel[Reporting Location City] ),
                        CALCULATE ( [Count Frequency], ALL ( InjuryCause[Cause Grouping] ) ),
                        ,
                        DESC,
                        SKIP
                    ),
                    ALL ( 'Legend colour code'[Lengend Case Grouping] )
                ) < 6
                    && [Top 5 by frequency and Incurred] < 6
                    && NOT ISBLANK ( [Count Frequency] ),
                1
            )
    )
RETURN
    COUNTROWS (
        CALCULATETABLE (
            VALUES ( 'InjuryCause'[Cause Grouping] ),
            FILTER ( _table, NOT ISBLANK ( [@Rows] ) )
        )
    )

Make sure "Maintain layer order is "on" under properties in the formatting pane - it will keep the legend visible once published even if you click on the chart.

And the visual will be interactive based on  a selection in the legend:

New file attached