Ironically, though the criticism of Hegel's negation of the negation was the path by which Marx claimed to be scientific, he did so by adopting Hegel's scientific gnosticism.

That is, Hegel's concept of Vernunft was the high-level science which goes beyond mere understanding (high level perspective vs practiced science). It is simply because Marx believed he was practicing the dialectic on materialism that his desire to use historicism (thinking you know where the future is progressing towards) could be satisfied without coming to see himself as a mystic.

Even more ironically, Marx still did predicate his historicist prophecy on the negation of the negation.

First, a summary of Hegel's negation of the negation:

Problem: How does the universal truth of reality come to be actualized?

Thesis - The idea (abstract)
Antithesis - ??
Synthesis  - ??

Let's do another dialectical synthesis to find the antithesis!

Thesis - Abstract
Antithesis - Negative
Synthesis - Concrete

The concretization of the idea is both an expression of the abstract's concept, while also being that which is not abstract - it is simultaneously the abstraction and not the abstraction.

Back to the ultimate dialectic (representing the entirety of the world process):

Thesis - The idea (abstract)
Antithesis - Concrete (substance, that which is finite, that of the senses/sensuous)
Synthesis - Absolute (that which comprises all of it - the idea, and all that there is and was in the physical world)

So here is what Feurbach and Marx criticized. The concept of an absolute is still an abstract one. The concrete, sensuous world and its historical process are tangible and material. They are without the mystical elements and are therefore those things upon which to philosophize.

Returning back to an abstract concept, under the assumption that this is a real thing that will come to be, is an affirmation of the philosophy based on that which cannot yet be certain.

But Marx does this too!

He says we're going to take the materialist process, and the tools by which Man has transformed nature to become more human (improving technology), and retain the good parts while negating the aspects which lead to domination and estrangement.

Thesis - man creates the world
Antithesis - man estranges man
Synthesis - man creates the world where he is liberated

But we're assuming that world is going to be created.

Put another way:

Thesis - capitalism
Antithesis - dictatorship of the proletariat (Socialism)
Synthesis - Communism

Thi synthesis is precisely the negation of the negation. Capitalism gave man technology and better living tandards, so we're going to destroy capitalism by brute forcing the ownership of everything by everyone (and thus no one). This allows you to keep all the good technology and then your expectation is that the negation of capitalism and property ownership is now going to magically be negated (the bruce force required to take it all over and administer the new state will spontaneously disappear), and you'll be left with the Utopia where we all have the benefits of technology, the benefits of people having access to the infrastructure that's been edified, and none of the estrangement or a need for a state, by virtue of the fact that everyone's needs are now met.

This helps us to grasp the headspace possessed when putting faith in the negation of the negation - something which occurs when we expect things that don't yet exist or things that might even be impossible.

So, when it comes to the negation of the negation, we have an evolution:

Hegel's Idealism -> Frankfurt school's dialectic on culture and the economy -> The feminists' dialectic of Patricharchy (brute force their own system to ellide the oppression of Patriarchy) -> CRT with race essentialism (using Structural Determinism and a Rousseauian critique of the master-slace dialectic to both claim race to be non-essential/social construction as well as something that is essential) -> Queer theorists with normativity and their own normalization -> Intersectional feminists with identity as a whole, since we can never have authentic identities in this world (as it currently stands).

AND NOW

Covidists, where we achieve immortality by fucking killing ourselves. We achieve optimal health by becoming unhealthy for the overall process of moving history forward towards our immortal endpoint.