Probably very niche but you could get into meshtastic. Most people who own a node a pretty interested in tech.
Edit:
You should probably check meshmap.net first before buying a device
You might want to look into smaller Lemmy instances that ask users to apply to join. Small instances can have pretty tight communities and you can meet people. People aren’t as faceless as they are on larger instances.
I think they mean like IRC, Matrix, or Discord: real-time chat rather than asynchronous. They may mean such a thing integrated into a Lemmy client, but it's pretty unclear in the original question.
That's less about the app and more about the community I would say. I get into those kinds of discussions on freenode (irc) but also on some old school web forums. I'm not hip enough for Matrix but I guess it has some users too.