I think it depends on how you use them.

I spend a lot of time lurking on Lemmy. I read discussions. I don't post or comment much. There's no social element to that experience. (This is an indictment of me, not Lemmy.)

I just recently rejoined Mastodon, and there I find myself replying to people's posts and having short discussions even though I don't "know" anyone. It's not "community" at this stage, but it could become that if I continue using the platform that way. And when I made a post introducing myself, there were several comments offering direction toward finding "my people" (a.k.a. community) on that platform. It's just up to me to make it happen.