Our forum provider has made a universal change to the functionality of how categories work. In the past, you could hide an entire category which would not only make the category disappear from view but it would also make discussions from that category disappear from recent discussions.
The new functionality offers the option to follow or unfollow a category. When you unfollow a category, you will still see it in the list of available categories; it just won't show up in recent discussions. (Unless you select "All" on the Recent Discussions page)
To follow a Category, click the Bell icon while browsing its page. You can also follow a category by clicking the ellipsis (•••) symbol to the right of its name while on the Categories page.
Finally, you can select between viewing All categories or only your Followed categories via the drop-down pictured below.