Yeah, you used to be able to dive into really interesting/useful discussions (pretty much a forum) about nuances of certain phrases/words, usually involving people who have grown up speaking the respective language. It was really helpful to get that extra detail and context on weird little quirks that may not have been obvious by the content built into Duolingo itself.
It was fairly recent, maybe in the last 3-4 months. I know for much of 2023 I would get the mini threads for some (not all) questions, but now I don't get them for any question. I agree it's a shame, because they really were the most educational thing on the app.