Mailing list
Long-form discussion happens on the mailing list.
The Idris source is available from our repository. Tools and code by the wider Idris community are available in a GitHub organisation.
There is an Idris community on Discord with several channels for learning, help and different aspects of development. You can get an invitation to join here This is currently probably the most active place for interactive discussion of Idris.
There is also an irc channel #idris on libera. Point your irc client to then /join #idris. For a web interface, you can try IRCCloud.
There is an active #idris channel on the Functional Programming Slack.

All participants in these forums are requested to abide by the community standards.