The dropdown that you are seeing with the words “all”, “none”, and “wordpress” is the subcategory selector for the Support category:
If you select “all”, then all the latest support topics will be displayed in the topic list. If you select “none”, then only topics from the parent category (support) will be displayed. If you select “wordpress”, then only topics from the support/wordpress category will be displayed. The “wordpress” category is a subcategory of this site’s “support” category. It is meant for topics that are related to Discourse/WordPress integration.