Free will is a metaphysical question that science cannot address. It can rule out some false claims about it, like some historical religious claims, but not the basic metaphysical question. Over time science will only build more and more specific explanations that show minds to be contingent on biological, chemical, physical, mechanisms and a relatively straightforward framework of causal reality. It will seem to narrow down the possibility for free will because it makes the space occupied by a ghost in the machine smaller and more fringe, but this is drawing too much from the religious tradition of blurring metaphysical and scientifically investigable questions - it will address only those hypotheses that confuse the two the same way it addresses the falsehood of all animals being created in their current forms all at once.

The kind of thinking you're referring to is called vulgar materialism by Marxists and Marx and Engels specifically criticized it; it's incompatible with the basic Marxist framing of political organization. Lenin famously derogatorily referenced the quote, "the brain secretes thought in the same way as the liver secretes bile" and spent a lot of time crapping on it.

Vulgar materialism lends a helping hand to the ruling class as it gives a definitive answer to the question of whether you "should" decide to politically organize and foment revolution: "no and your question is invalid because you can't choose to do anything". Dialectical materialism is a direct response to both an idealistic dialectic (Hegel) and vulgar materialists (positivist-inclined liberals).