We have tested several forum platforms, and they all seem to support some form of this. Where a user might not have access to a category or read a topic, but they can see they exist. They can even see the topic titles in latest, but when they click they are told they don’t have access to that forum or topic. bbpress, nodebb and ipb allows this, but I can’t seem to figure out how to do it in discourse.
If you’re asking “Why on earth would you want to do that?” because we have a wealth of content in private forums that we want non-members to know about, to entice them to join, otherwise they are only seeing the tip of the iceberg. Thoughts?