That's why I put Discourse first.
> I am not sure whether anything from the Racket Discourse forum is findable via search engines.
It is.
> There used to be the Google groups thingy including a mailing list.
The mailing list is still running. But people have moved on to Discourse. You can configure Discourse to send you digest mails, if you prefer mailing lists.
Personally, I liked the mailing list. However, forums such as Discourse have replaced the role of the mailing list. See the forums for Swift, Rust, Processing, etc. They have all moved on to Discourse.
I was a long-time skeptic of moving away from the Google Groups list, so I try to be equally vocal in saying that the move to Discourse was handled really well IMO. In fact it is not "a JS-only forum": you do need to sign up in the web UI, but, after that, you can put it in "mailing-list mode" and ignore the website completely, including for starting new threads (see <https://racket.discourse.group/t/how-to-enable-mailing-list-...>). The email interface is important to many Racketeers; if other Discourse instances don't enable it, that's their admin's choice. The Google Groups list had been rendered nearly unusable by spam, and it was never free and open-source software, which Discourse is. (I wrote more detailed thoughts at the time in <https://groups.google.com/g/racket-users/c/RnIAQnZpvh0/m/A78...>.)
On the other hand, I share some of your concerns about Discord (the similar names are unfortunate). But there was never an organized "move to Discord": some people just started talking about Racket there, as people had before, and still do, on IRC and Slack and all sorts of places. People are also regularly nudged to move non-transient conversations to searchable and archived venues.
It would be great to have a way of communication again, that does not require JS or Google or Discord or any other closed thing or walled garden. Especially for a programming language. Of those listed JS is probably the smallest inconvenience, so if I had a question now, I would probably prefer going to the damn discourse thing to ask it, rather than joining the Discord server.