Here are some communities I’ve found where people discuss Hugo. They all just happen to be in Slack. None of them supplant the forums in any way, they’re just people chatting. This is not a commentary or discussion on the need for any additional Hugo support channels, thank you.
The #hugo channel in the Go Slack.
The New Dynamic (about static site generators in general) Slack (this is my slack).
Forestry.io (a commercial editor for Hugo sites) Slack.
The #static-site-generator channel in the Write the Docs Slack.