I disagree. By definition social media is “new media technology that facitilates the creation, sharing and aggregation of content amongst virtual communities and networks” so Reddit and Lemmy are social networks.

There are several subkinds of social networks some are worse for kids (and adults) than others. Most sites in the internet don’t allow users to create and share content, online newspaper only may allow users to comment but the content comes from “journalists” and collaborators.

Discord is used like a forum though, with chat capabilities but it’s social at it’s core.