Variables in Custom Question

I am creating a Dashboard that contains filters, but I am unable to use them with questions created using Custom Question GUI.
The filters works only with question made with Native Query and variables (SQL parameters).

Is there a way to apply Dashboard filters to questions created with Custom Question GUI ?

In the data model, you set the Type of the field to Category. This allows it to be used as a filter in the dashboard. Below shows a dashboard in Edit mode. 4 parameters, the first one being editted. You can see that each question has the parameter name set. Clicking the question allows you to change to a different field.

Were the questions “Total Product” and “Distinct Supplierid” created using Custom Question or Native Query ?

If they were created using Custom Question, where did you define “Country” parameter ?

Custom question. No parameter needs to be defined.

when I select “Add a Filter”, then “Other categories”, the questions built with “Custom question” show “No valid fields”.

These questions are summarized values that use row visualization.

How can I add filter for them ?