the “dismiss new” tab only dismisses all posts considered “new” by the user within the new tab. It would also remove the blue new icon counter from the category view as well. ) “Mark all as read” is not currently implemented into discourse.
A post is considered new when it’s been created in the last 48 hours. ( User configurable located here: Account --> Profile --> Notifications: “Consider topics new when:” )
A post is considered “unread” if the user created the post, replied, or spent over four minutes on the post. It does not mean posts/topics you’ve NEVER read.
Ways to be notified of certain new posts: ( On a per category/tag basis )
Tags/categories - you may go to User profile --> account --> tags/categories:
You could enter the relevant tag here, or use the categories above it. Any tags/categories set here to tracked/watched will inform the user of new posts / updates.
If you go to the search bar at the top and hit “options” an advanced search pops up, it allows the user to search on a read / unread basis ( along with all of the other statuses in the forums, pinned, by user, tracked etc). Along with categories/tags as well.
I could use this filter to quickly find all un-read posts in a particular category, with a time frame as well.
Let me know if this was any use to you in regards to the problem.