I think I saw someone else mentioned that bug as well. I think your subscription list in the main menu doesn’t automatically refresh after you subscribe to a new community so currently you would have to close and reopen the app. Updates and bug fixes have been daily lately so hopefully that gets fixed soon.
It’s an app-specific feature so using another app or viewing through your browser would not have the feature. Hopefully it’s baked into Lemmy/Kbin itself in the near future so users can manage it across access points, like blocking of users or communities.