This measure calculates the running max/min/average (depending on your requirement) of a running total based on the dynamic date range selected.
To recap, here is the Running Total quick measure that Power BI gives us. A measure like this should be be present in your model.
Running Total :=
ISONORAFTER('Date'[Date], MAX('Date'[Date]), DESC)
Below is an example of how to set up a running MAX of the running total shown above:
Max of Running Total :=
VAR __INTERIM_CALC =
SUMMARIZE ( ALLSELECTED ( 'Date' ), 'Date'[Date] ),
"__RunningTotal", [Running Total]
ISONORAFTER ( 'Date'[Date], MAX ( 'Date'[Date] ), DESC )
To find the running average/minimum/etc. of the running total, just change the MAXX in the above query to AVERAGEX, MINX, or another AGGX function.