Community rooms live in the Academy: join the ones relevant to you. Some rooms are gated by plan or by completing certain modules.
Each room has its own notification level, set from the room's bell icon:
All: every message notifies you.
Mentions: only @you mentions, @everyone, and replies to your messages.
Muted: no pushes at all (the room still shows an unread dot).
Moderators can post announcements with @everyone: these reach everyone except muted members.