For what it's worth, I agree with you about Lemmy (and Reddit) not really qualifying as "social media." I think of it more as a spectrum than a binary value...

• Old school forums were very specific to a single topic (though most forums I used did have an "Off Topic" board), and only lightly social -- I never knew any forum user outside of their respective forum, and certainly not in real life.
• On the opposite end, Facebook/Insta/TikTok are very social -- there's a lot of expectation that you'll be interacting with people that you know personally -- and they are more "agnostic" (?) of any one particular topic.
• Reddit and Lemmy land somewhere in between those two extremes, in terms of both the social and topical aspects. But neither cross the line into "social media," at least not for me and my personal definition of the term.

And just to split hairs even a little more, I think Lemmy is more palatable* than Reddit for me, by virtue of the smaller (and generally more tech-savvy) user base.

E: Spelling (thank you, WelcomeBear!)

Lemmy is a media that allows you to be social.

Forums are also social media.

You kids, ha. I'm hitting 40 soon, and Lemmy is absolutely as much social media as Reddit is, just different scale and technological underpinning. Don't be high and mighty about it, you can easily burn as much time scrolling through Lemmy communities.

That's like saying Twitter isn't social media because its a microblog. Lemmy is definitely social media. We have profiles, can add each other as friends, send private messages, etc. It's not structured the same as most other social media websites, but it is social media

No matter how much you rationalise it, forum is still a social media. You are still socialising after all-- in a medium of communication. You can still post pictures in forums if you want, but modern social platforms just have better UI and convenience to post videos and photos than older forums.