Depends on the server you’re on. Lemmy found popularity when a group of communists had their subreddit(s)banned. Lemmygrad is worse than Lemmy.ml but both are managed by the same people and both have a clear communist bias because of the way the project came to be. The .ml in the domain name may technically be the country code of Mali, but the project is hosted under that domain because the letters reference two famous communist names.

Other lemmy servers are less obviously left wing. They’re still relatively left wing, but less anarcho-communist. Some are right-wing, but unfortunately the ring wing servers seem to attracts disfranchised right wingers who are often banned for good reason.

I’d say FOSS advocacy has a left wing bias, though a lot of people who use open source because of personal freedom aren’t necessarily left wing. Plus, the biggest open source projects are all backed by huge capitalist companies, so I don’t think the connection between open source software itself and the left is that strong; I think it’s mostly the advocacy groups and activist communities that tend to go that route.