Hi Jheng,
You could create a helper table which stores all dates in a separate table. One of the columns in this table could be in format "YYYY-MM”.
You can create a reference from this date table to your relevant table.
Via Subjects > Columns > <your_date_column> you can configure a lookup which shows for example the "YYYY-MM” field from the lookup table you just made. This will become a dropdown list in a filter form / popup.
Having a helper table for dates is super helpful in many other situations as well!
Does this help your case?
Best regards,
Nick Janssen