Lemmy.ml is maintained by the Lemmy developers, who are Marxist-Leninists. As a consequence, many users of Lemmy.ml are Marxists of some stripe or Anarchists. Moderation generally favors Marxism, and favors AES states, and does not tolerate Zionism or chauvanism, etc.
Some of the other instances disagree with this general slant on ideological grounds, and have also defederated from Hexbear.net and Lemmygrad.ml, the 2 largest explicitly Leftist instances, so there is frequently sabre rattling.
If you want to learn more about Marxism-Leninism, I keep a Marxist-Leninist introductory reading guide. You can check it out and see if Lemmy.ml is a good fit for you or not. I use it because it's more broadly federated than a generalist instance like Lemmy.world, and also has a good number of Leftists. I also use Hexbear.net.