He constantly frames things vis-a-vis the freedom of workers and their having input in their government. Does that sound like China to you, or Cambodia under the Khmer?

How, exactly, does he frame them? Can you give an example? China practices Whole Process People's Democracy, which absolutely isn't liberal democracy, but does have more worker participation than Capitalist states.

As for Cambodia, the Khmer denounced Marx and were stopped by the Vietnamese Communists, no Communist supports the Khmer Rouge. No, what Marx described was not adopted by Cambodia, because the Khmer Rouge denounced Marx.

Sure, but what he didn't advocate for is for a new form of aristocracy to emerge from within workers' ranks. I think this was Bakunin, not Marx, but the dangers of "labour aristocracy" were already known at the time.

You're confused on a few things here, the Labor Aristocracy is the Proletariat that makes more than the median wages in the global context due to the impacts of Imperialism, ie in the US median Proletarian wages far exceed that of wages in Chad not because the US Proletariat magically creates more value, but because wages are higher due to vast exploitation of the Global South.

Secondly, there was not a "new form of aristocracy" in AES states. AES presented an increase in democratization, including practices like instant recall elections, and units electing delegates. These delegates weren't hereditary, had to be elected, and could be recalled at any time.

I've read David Harvey's synopsis of Capital (because life is too short to read the whole thing), Gotha, and of course the Manifesto. I'm actually puzzled that you see Gotha as advocating for authoritarianism. He talks about the eradication of class and about how people should not be "ruled". Both of those things are endemic to current-day communism. I just can't imagine that Marx would look at the way the CCP operates and think that was an accurate reflection of his personal politics.

Critique of the Gotha Programme isn't advocating for "authoritarianism," nobody does. Critique of the Gotha Programme advocates for centralization, also alluded to by the "ceasing of the anarchy of Capitalist production." Marx clearly crituques the vagueness of the Gotha Programme in question, along with its flawed conception of the state.

The question then arises: What transformation will the state undergo in communist society? In other words, what social functions will remain in existence there that are analogous to present state functions? This question can only be answered scientifically, and one does not get a flea-hop nearer to the problem by a thousand-fold combination of the word 'people' with the word 'state'.

Between capitalist and communist society there lies the period of the revolutionary transformation of the one into the other. Corresponding to this is also a political transition period in which the state can be nothing but the revolutionary dictatorship of the proletariat.

Now the program does not deal with this nor with the future state of communist society.

Engels elaborates in Socialism: Utopian and Scientific (itself a phenomenal work that I highly recommend reading after this conversation), what form of government a Communist society would look like as Marx alludes to in Gotha:

When, at last, it becomes the real representative of the whole of society, it renders itself unnecessary. As soon as there is no longer any social class to be held in subjection; as soon as class rule, and the individual struggle for existence based upon our present anarchy in production, with the collisions and excesses arising from these, are removed, nothing more remains to be repressed, and a special repressive force, a State, is no longer necessary. The first act by virtue of which the State really constitutes itself the representative of the whole of society — the taking possession of the means of production in the name of society — this is, at the same time, its last independent act as a State. State interference in social relations becomes, in one domain after another, superfluous, and then dies out of itself; the government of persons is replaced by the administration of things, and by the conduct of processes of production. The State is not "abolished". It dies out. This gives the measure of the value of the phrase: "a free State", both as to its justifiable use at times by agitators, and as to its ultimate scientific insufficiency; and also of the demands of the so-called anarchists for the abolition of the State out of hand.

You can see that, rather than the anarchy of decentralization, Marx and Engels advocated for centralization. The "centralized" society has no State, but it does have an Administration of Things. Think the Post-Office, and how it still has managers and administrators. These structures remain even into Communism, after Socialism, yet they aren't considered a "state" by Marx nor Engels.