This idea has been merged into another idea. To comment or vote on this idea, please visit APP-I-1471 Ideas portal: Filter by custom fields.
We can use categories as filter in the portal with "idea categorie" but it is not a required field.
We can create categories with "custom field" to make it required but it cannot be used like a filter in the portal.
It would be interesting to have one fields which is at the same time required and usable as filter in the portal.