I'm glad to hear that and I wonder what I am missing. How have you found your way into community there?
In my (limited) experience with Discord, it has worked exactly like a group chat: each "server" has its own fixed membership, and there does not appear to be any larger community. People don't come and go; I have never met anyone on a discord channel who wasn't already part of the group.
Telegram I have never tried; I thought it was a WhatsApp competitor, and I don't know anyone who uses it.
I don't use telegram, but I know others who do, and there are certainly general group chats, though I mostly hear about conspiracy people and crypto.
For discord, it's always an external community for my servers. Either software (home assistant, and a related software netdaemon), a metal review blog (angry metal guy), a game company (owlcat) or a twitch stream (a food truck and a cooking stream). Only my TTRPG group is a closed group.
I miss being part of something that felt like a community. I don't know where to find that anymore.