The accepted and preferred means of communication is our Discord server. Most Fabric-related discussions and announcements can be found there, and you're most likely to get help with modding-related questions and issues there, too.

As an alternative you can use GitHub Discussions, but beware that response times and community engagement will likely be lacking in comparison.

There also exists the #fabric IRC channel at EsperNet (irc.esper.net). It's not actively used though and should be seen as a historic relic. You can access it using an IRC client (such as HexChat) or by using a web browser.