Discord is more of a social media platform than a messaging platform, everything you do on there should be treated as public, it's literally designed for rooms for tens of thousands of people to talk in. Sites like these have existed for years.

People do the same mistakes with Matrix as well, although you can just look at the web preview of rooms with no account, and encryption is useless in big rooms if anyone can join and watch.

We was able to watch an approve-only Discord server for forensics analysts (employees of *those* companies) and law enforcement because they kept the room preview open. They sounded pretty annoyed about GrapheneOS too...