Row grand totals - Profitbase/PowerBI-visuals-FinancialReportingMatrix GitHub Wiki
Enabling the Row grand total option in the Totals section of the Format pane adds a grand total row to the bottom of the visual, containing the sum for each column.

Freeze grand totals:
New from v8.3
Toggle on this option, and the Grand total row will always show as the last visible row in the matrix: