I agree that there is a difference in how sites like Facebook and Twitter operate vs Reddit and Lemmy, BUT I think they’re still both social media. One tends to emphasize personality and individuals more. You’re encouraged to Follow/Like/Subscribe to the people or accounts themselves. People are given big avatar images and/or profile pages, you can see who they’re following. The topics themselves aren’t as important, it’s more about, “What will Taylor Swift or Elon Musk say today?”. Individuals are given much more attention.

Contrast that with Reddit/Lemmy/forums, where people are more or less reduced to a name, less-emphasized avatars and minimal profile pages. The topics themselves are emphasized and typically communities as a whole come together and do things as a group (meme wars and whathaveyou). The individual is less important and the communities/subreddits are more the “stars” of these sites.

I think in both cases they’re still “social media”, but they are definitely in different categories and they emphasize different parts of the experience.