These look like a weird mix of Slack threads (temporary (though not enforced in Slack), written in sidebar) and Zulip threads/topics (named, available in the channel list), though... with downsides compared to both (for example, you can't forward messages to original channel like you could on Slack). Feels a bit awkward, but time will tell. My main concern right now is with discoverability and moderation - it seems a…
As a Discord moderator (discord.gg/wilbur, 310k+) who's used Threads for a few months now while testing, there's a specific Threads button that lists all open threads - even private ones, although behind a toggle - and that works pretty okay. Most large servers only use Threads internally within staff teams, not in the wider general channels yet, though!
I can see there's a Threads button next to the search bar, but it appears to be scoped to the channel I'm in; I don't see a way to see threads across all channels.