Marx wasn't really right about anything, not to mention his center piece grand theory.
He predicted history would take us the triump of the proletariat then stop. There is no sign of this happening. Not only that he concluded it would happen in the most advanced economies first in the end of capitalism. Wrong again. The revolutions happened in less developed places...china and Russia.
He predicted that capitalism would drive down wages to survival level before its final denouement. In fact as economies became more advanced, both wages and living standards rose to levels not even dreamt of in Marx's day or that he could even conceive. This guy had zero idea of innovation. He was clueless to understand capitalism changes and evolves. The same way humans progress, we solve problems by adapting our practices to new circumstances. He never considered this.
Also he didn't understand basic economics. He claimed that the value of a thing arises from the labor put into producing it. No. It's based on demand. I can spend eternity making something, if no one wants it, it's worthless.
I can go on forever about the guy who's responsible for millions of agonizing deaths.