IMO Lemmy's a new version of old-school web forums and link aggregators (which have been around since the beginning- kind of like Fark, Slashdot, etc). Using this site feels the same as using those sites.
Think social media's a very specific thing that started off in the early-to-mid 00s- i.e., a site / app where you keep a profile that's tied to your real-life identity and real-life social circles (myspace, friendster, linkedin, facebook). And that's where the harm kicks in, since suddenly you have to worry about having some kind of curated digital persona, which has some kind of real-life impact. So if we can't talk about the harms of social media in a specific way (i.e., the harm of constantly comparing your life to these idealized representations of other people's lives), then 'social media' isn't a meaningful term anymore.