The closed space of a group chat with friends worsens the loneliness epidemic? And arguing with random strangers on Reddit alleviates it? It's very much the opposite. Big, open and often anonymous social spaces are terrible at making you feel part of a group. Spaces with few people who you actually know and like and can depend on are key to not feeling lonely, and yes they tend to be closed.

Exactly, the reason that people feel so alone is because of void "interactions" on social media.

Closed doesn't mean undiscoverable. The biggest closed group chat I'm in is the Telegram channel for a podcast I listen to, and it's plugged in every episode. Discord has issues, but group chats there are still mostly fed by public activity like subreddits or YouTube channels.

Closed just means you can't open a page and read the full history like a forum. It doesn't mean it's only knowable to people currently inside and people they invite.