I really dislike using Discord and I can't even figure out why (so it's probably me). I do know it's not the part where it is a chat app per se - I'm happily using Zulip, managing with Slack, and WhatsApp, Telegram and Slack all have their place. But something about the UI/UX of chatting in Discord just makes it a stream of conversations where I can barely follow what's going on.

Having said that in many contexts a forum with threads that have a clear topic are just so much more of an appropriate solution than chat apps. I don't understand why people prefer the latter (although it does explain why I prefer Zulip since it manages to be a good hybrid in how it organizes discussions).

I'm in the same camp, discord and discourse just aren't useful to me

My number one issue with most of those forum "successors" is that everything is hidden behind a registration wall.

That means that they won't be indexed by search engines, so I cannot serendipitously stumble across them during a random web search in the first place, and even if I somehow learned about them, having to sign up merely to read some stuff is annoying.

Isn't that also true for Facebook groups?

I don't really like Discord, so I don't use it, and have no feedback on it.

I used to run a SimpleMachines forum, and we actually wanted to prevent the contents from being indexed.

I agree - very easy to lose track of something in the random chat that occurs. I use Discord because there's where some discussion I'm interested in happens though - not much choice sometimes.