I wish FOSS communities that want an alternative to Discord or Slack ditched Matrix altogeter. It sucks for that. Better use Zulip or Mattermost, both of which are self-hostable.
Edit: I looked up and apparently Mattermost would be out of the question for their feature downgrades in the community version as of late...
Correct me if I'm wrong but I believe Zulip's licensing de facto restrict self-hosting solution for 10 users (others won't see notifications on their mobiles or something like that). This is important for non-commercial communities.
No. See the "Sponsorship and discounts" section on the pricing page, which makes clear the 10 users limit for free usage of the mobile notifications service is for workplace use, not communities.
Edit: I looked up and apparently Mattermost would be out of the question for their feature downgrades in the community version as of late...