Sorry, maybe I misunderstood your problem. I had the impression you were talking about inline oneboxes.
Quote from the second link:
Steps to reproduce
- Create a new Topic on https://discourse.gnome.org/.
- Type some text, and without going to the next line, add an external link, like Automatic cross-links. In the preview pane, it should appear as
Automatic cross-links - feature - Discourse Meta.- Still without going to the next line, add an internal link, like Flag posts as a solution in the Community category - Site Feedback - GNOME Discourse. In the preview pane, it should appear as
https://discourse.gnome.org/t/flag-posts-as-a-solution-in-the-community-category/20236.
A featured link is added to a topic when you paste a link into the title field of a topic before writing anything else. Then the link is added next to the topic title, which is also visible in topic lists.
When you post a link in the same line as text and it is replaced by something more readable than the URL, it’s an inline onebox.
Because your steps to reproduce mention typing text before posting the link, I changed the tag. I will gladly change the tag back if you meant featured links and not inline oneboxes.
Then the answer is probably simple: Featured links don’t work for internal links. So you cannot create a featured link for the forum you are currently posting to.