There is almost nothing going on in the world that could classify as real leftwing extremism. Every few decades some cars get light on fire at a political event and that's about it. In Germany the RAF is still the example for the radical left after like 3 or 4 decades of nothing happening because they don't have new examples. They shot some politicians in the 70s and 80s. There hasn't been anything like that since. Everything you hear about the extrem left is basically propaganda by the right and capitalists. If you want to see right wing extremism it is probably sufficient to watch the damn news. The overton window has now made fascism normal. People are just going with it because people always are going with what the "current thing" is.

Mass proscriptions, seizing of major companies, either nationalizing or returning them to worker control, etc...

Radical left is various things depending on the group. Like, there is no common agreement among them. Flavours include Communism/Marxism, Anarchy, unlimited unchecked migration, pacifists, hating police, forcing everyone to altruism.

Radical leftwing politics is stuff like this.

Bro... Don't be a meme.

Extreme left wing would be nationalizing Silicon Valley and then putting them under UN command.

It would still benefit the world at large, even the americans.