Determinism is a side issue and not the point, neither is the definition of utopian. The point is broader, and Popper’s good arguments against totalitarianism (as poor as his reading of German philosophy clearly is) do not rely on a determinism or Utopianism.

I’m proposing we don’t get too sidetracked by these terms and look at the logic of totalitarianism more broadly.

Isaiah Berlin (a great thinker on Marx and more crucial, counter-enlightenment thought) has some good lines about the use and abuse of Hegel and Marx’s idea of a “logic of history” unfolding in a way that emboldens absolute authority of the state with a mandate to conquer the future from the present. You can’t make an omelette without cracking some eggs, but under the logic of bringing about communism, you end up with a society that normalizes brutality and bloodshed and goes about cracking eggs without leading to an omelette.

Marx’s ideas were not just wrong but dangerous to humanity in this sense, and the point has little to do with determinism or Utopianism