In Ovidentia version 3.2:
Log in as a user with administration rights.
In the "Administration" section select "Topic categories" in order to get the "topics categories list".
You should at least have the default category in this list. And others if you have created additional topic categories.
In this "topics categories list", select a category that should have a topic that is visible for unregistered users. This displays a page tittled "Modify topic category". Check that the "Enabled" field has value "Yes". If not, set it to "Yes" and click the "Modify" button. This brings you back to the preceeding page so you again select the topic category in order to come back to the "Modify topic category page".
Now on the menu bar, select the "Topics" command. This displays a page titled "List of all topics [xxx]", where xxx is the name of your topic category.
If this list is empty, you have to create a topic first.
If there are topics in this list, select a topic that should be visible for unregistered users. This displays the "Modify a topic" page.
On the menu bar, select the "view" command. This displays a drop down menu where you select "Everybody" or "Unregistered Users" and you click the "Update Groups" button.
You now have a topic that is visible for the unregistered visitors.