Custom filtering in backend? How to do?

Hi,
While migrating an existing fabrik based website into flexicontent I faced an issue due to some limitations in old fabrik app. I must inspect and change quite a number of items in flexicontent now manually. I changed these items in state "in progress published".
For this case I used type "tuinlogboekdetail" with category "tuinlogboekdetail".  In backend  Items-list I would like to select a subset of the items based on a field "jaarmaand". The current layout is in attachment  "Custom filter 1".
I added the columns "datum" and  "jaarmaand" in type definition (tab items manager)  in field Custom columns (see attachment "Custom filter 3").
I expect in field custom filters available filters. Imho I set the filter for field "jaarmaand" in field definition as in attachment "Custom filter 2".
What is wrong with my approach and how can I get  filtering available in backend. (in frontend it is available, but not very handy)
Regards HenkKV
 

hello
1 if you set subtype that disable type tab in items list
2 you can allow filter in your screen 4 (custom filter that display filter in dropdown (filter icon after search)