I don't see it that differently to using GitHub for hosting the code. In terms of privacy at least it's fairly clear to users, wanting to chat, that their data and content will be owned by discord. Users have the choice to enter the chat or not, it's not required to browse the website or use the software.
Using GitHub is also bad, for similar reasons, even leaving aside the fact that Microsoft provides services to those who operate concentration camps.
Gitea, Mattermost, and Discourse (not Discord), all self-hosted, will serve your community better in the long run.
Icewhale is doing a custom dev board - zimaboard - and this is their sideproject as best as I can tell. Think they may have gotten bored halfway through waiting for chip shortage to go away.