Native Federation is currently in Alpha and not recommended for production use. Expect breaking changes and limited functionality. Use in testing environments only.
To invite an external user from another federated server to a DM, multi-user DM, or channel, use their full federated address when adding them as a member.
Federated user format
@username:server.domain
Notes:
Federated users cannot currently be deleted from workspaces (as of version 6.12).
The same syntax applies to all federated rooms, whether DMs, group DMs, or channels.