Subscribe to category from Mastodon - no activity?

<p>Hello,</p> <p>just recently found out that NodeBB supports ActivityStream, great! We are running the Forum for UBports and Ubuntu Touch at <a href="https://forums.ubports.com/" rel="nofollow ugc">https://forums.ubports.com</a> and my first idea was that I could make the News category discoverable for the Fediverse.</p> <p>So after some fiddling I managed to publish <a href="https://forums.ubports.com/category/41/news" rel="nofollow ugc">https://forums.ubports.com/category/41/news</a> correctly it seems, as I can search, see and subscribe this from Mastodon:</p> <p><img src="https://community.nodebb.org/assets/uploads/files/1766089201890-813d4781-0373-48a9-a376-72cdd7de27ac-grafik.png" alt="813d4781-0373-48a9-a376-72cdd7de27ac-grafik.png" /></p> <p>But so far no new posts do appear.</p>