Django filtering error: annotate + distinct not implemented

Question

I'm using Django 2.2 and I need to group a query set by month and count the number of rows

Input:

Id | Value | Date

1  | Example value 1 | 2020-02-10
2  | Example value 2 | 2020-02-17
3  | Example value 3 | 2020-03-21
4  | Example value 4 | 2020-04-15 

Expected output

Month | Count

2020-02 | 2 
2020-03 | 1
2020-04 | 1

I'm using an initial filtering like this.

details = Process.objects.filter(started_at__gte=start_date, finished_at__lte=end_date).order_by('-serial_number').distinct('serial_number')
#Some code using all details
#Filtering 

After that I need to do the group by and count.

summary = (details
          .annotate(m=Month('started_at'))
          .values('m')
          .annotate(total=Count('id'))
          .order_by('id').distinct('m','id'))

But when I execute it I got the following error:

NotImplementedError: annotate() + distinct(fields) is not implemented.

Month class definition:

class Month(F):
    function = 'EXTRACT'
    template = '%(function)s(MONTH from %(expressions)s)'
    output_field = models.IntegerField()

I'm trying to do something like this.

Django: Query Group By Month