We don't have a setting in the ACP to exclude a category from /recent and /unread right now. Users can ignore a category and it will not show up on those pages.

If you don't have a lot of categories you can also change the url of /recent and /unread to include a list of category ids.

Let say you have categories 1,2,3 and 4 and you don't want to show category 4 in /recent and /unread then you can change the navigation urls to /recent?cid[]=1&cid[]=2&cid[]=3 and /unread?cid[]=1&cid[]=2&cid[]=3 respectively. Navigations items can be edited at /admin/settings/navigation

NodeBB doesn't have an ACP switch that lets you leave a category out of unread/recent. There is user-level ignore, but it's not required and you have to choose to use it.

To fix the problem quickly, change the nav URLs to include explicit cid[] filters so that the noisy category is not included in /recent and /unread. If your categories don't change often, it works fine.

The right fix is a small NodeBB plugin that filters topics.getRecent / topics.getUnread and delete that category on the server side. That's the only way to make it truly global right now.