If you want to look at the cases that are currently open, I recommend that you use something like
SUM(CASE WHEN PROCESS EQUALS ACT 1 END OR PROCESS EQUALS ACT2 END THEN 0 ELSE 1 END)
In a single KPI. The issue with displaying this metric over time is that cases can have activities in several months, which will be an issue when breaking them up by the dimension rows of eventtime. What comes closest will be something like:
COUNT(DISTINCT Activities.CASE_KEY) -
CASE WHEN (PROCESS EQUALS ‘Closing Activity A’ END
AND “_CEL_P2P_ACTIVITIES”.“ACTIVITY_EN” = ‘Closing Activity A’)
OR (PROCESS EQUALS ‘Closing Activity B’ END
AND “_CEL_P2P_ACTIVITIES”.“ACTIVITY_EN” = ‘Closing Activity B’)
OR (PROCESS EQUALS ‘Closing Activity C’ END
AND "YOUR ACTIVITY TABLE " = ‘Closing Activity C’)
THEN “YOUR ACTIVITY TABLE”."_CASE_KEY"
And Eventtime from the activity table as dimension. However you need to be aware that this will not include the cases which 1. are open and 2. did not have an activity in the individual month.