Is there a way in ETL/Reporting to show the cumulative total for every month

I'm trying to show a dashboard where in I need to show the cumulative sum of the user count for every month. Need to have the month listed for which there is no activity also.

In the above image, I have data for 2019-07-01 and then there is data for 2020-01-01. I also want to have data to show in between these months and show the data of previous available month's data in it, if nothing is there in previous month also then 0.

Populated the above cumulative data using the code below:

SELECT 	a.*, 
		CAST( (	
			SELECT 	SUM(case when `UserCount` is null then 0 else `UserCount` end) 
			from 	`transform_data_3` as b 
			where 	a.`MonthDate` >= b.`MonthDate` 
			and 	a.`Group Name` = b.`Group Name` 
          	AND 	a.`Overall Onboarding Status` = b.`Overall Onboarding Status` 

		) as signed) as 'MonthlyOnboardingCumulative' 
FROM `transform_data_3` a

Thanks in advance.

Srinivas