I thought "Communities" were already used to group rooms?
Anyway I searched more for these "Spaces" and I found this:
Spaces are particularly interesting because they open up the possibility of Matrix being more than just a big flat namespace of conversations: instead they provide a global fully decentralised hierarchical filesystem, complete with decentralised ACLs, allowing users to publish and curate an arbitrary taxonomy of whatever data they choose (be it real-time conversations, history, data streams, files, objects, etc). This has potential to flip Matrix entirely on its head: Spaces could become the main backbone of the protocol, with chatrooms being mere leaf nodes in a giant tree of collaboration.
While I hope in the long term Matrix ecosystem will suit all the use cases, even the social ones by replacing/complementing ActivityPub, at the moment even its flagship client that most people are mentioning (Element) can't replace Discord.
Instead I think the best alternative at the moment is Telegram because it has a large userbase, native clients for Linux, Android, Windows etc, voice chats that suit the Discord-like use case and it doesn't use/sell users' data.