Mastodon has definitely improved, but more to the point, there’s really nothing else. Particularly not anything that anyone is using. Unless you widen your definition to include Bluesky.

Honestly, I’d say that Mastodon’s perceived complexity in the past was kind of an illusion anyway. The problem of choosing a server was really made out to be this huge hurdle, when in fact it was no big deal at all; I was a member of several different servers over time, and I didn’t feel like my experience was substantially different on any of them. Just join one that seems interesting or is near you or whatever, and you’ll be fine. After that, it operates pretty much the same as Twitter did. Following people on other servers can be a little bit trickier on web, but in the app it’s pretty seamless.