I’ve never heard anyone before argue that Marx didn’t want the socialist transformation of the world he wrote about to actually happen.
Marx was a sort of Hegelian. Hegel believed in something he called the World Spirit, a sort of impersonal god which revealed itself more and more over time through history.
Marx believed in a materialist version of this idea, over time, there was an interaction between classes or social groups that would play out and go through certain stages, until it finally was fully formed and reached a sort of ideal state. He called this, after Hegel, a dialectic. Each of these social or economic stages contained problems or contradictions that would create a sort of crises or collapse, and then there would be a reformation that solved or brought together the contradiction into a higher form of society. This would go on until you reached the highest form that did not contain any more contradictions.
Some of his discussion is of historical examples of these stages and how they are true to his theory, and his discussion of capitalism is about what he thinks the contradictions are that will cause its failure. And then he also discusses what the resolution of that will be and the final state.
But the thing is, this is a historical process, you can't just come up with the final stage without going through the others because they are all important. None of the attempts at establishing actual communist states really even correspond to what Marx wrote. All of them involved peasant societies doing mainly agricultural work for example whereas Marx said the final society would come out of an industrialised kind of economy. And that was to be about the proletariate, the actual people themselves, owning their own labour, and the disappearance of the capitalist class. Not about some sort of elite group trying to force that to happen through state ownership of capital. That's not a historical dialectic. And if its not a historical dialectic its not Marx.