I've read almost no Marx, but the argument doesn't really rely on it, I think - the "working class" / "proletariat" in Marx's sense are the people whose economic power comes from the actual labor they do, as distinguished from the business (or land, or whatever)-owning class / "bourgeoisie", whose economic power comes from that ownership. Or, in other words, the working class are the people who make their money from operating the means of production instead of owning it.

(Note this is different from the usual definition of "working class" in popular politics as a euphemism for "lower-class". You can be making a six-figure salary and still be "working class" in this definition. If you're a highly-paid tech worker living with roommates in a rented San Francisco apartment, you're working class. As a corollary, "working class" doesn't mean you lack "privilege" - you can be quite powerful, but you're still less powerful than the owner class, and the whole narrative about buying a house / doing a startup / passive income / etc. is about slowly exiting the working class, because that additional power is meaningful and valuable.)

But basically the point is that a corporation is an amalgam of many actors, and it's worth figuring out which actors are doing what. "Corporations" don't, strictly speaking, have agency.

And it's the people who are owners who tend to be more conservative and the people who are laborers who tend to be more progressive, not the corporation as a whole. The corporation is driven by lots of pressures. Sure, it seems weird that corporations are espousing progressive causes when conservative views are better for corporations, but part of the weirdness is that the corporation doesn't have a single set of political views the way an individual person (kind of) does.

(Another case of this fallacy: "Google donated $n to this left-wing candidate, look at how Google is influencing politics." 99% of the time, Google didn't, individual employees did with their personal agency over their Google salary, and the owners did not.)

I believe it's true that a lot of the PR support is performative and coerced - but I believe what's going on is that it's coerced by the laborers who care, and in most cases (Coinbase being an exception) the corporate owners don't care terribly strongly about not being coerced into exhibiting that support. So the corporate Twitter account says something, written by a laborer in a way that avoids annoying the owner, and it comes out the way it does. It's profit-seeking in the sense that the owners want to placate the laborers so they keep working.

Or, in other words, it's not weird that an organization (whether a corporation or a spy agency or whatever) that is filled with a bunch of young educated professionals tends to occasionally make public statements that are consistent with the politics of young educated professionals as a group.

There's also a possibility that the PR support is the PR folks themselves being coerced by some outside force. I don't have evidence to disprove that, so yes, it's possible. But I think we'd need to very precisely name who that outside force might be.

One reason I think it's more likely that this is internal support is you can see the same pattern where there's no profit motive at play. A mainline/progressive church will put up a rainbow flag and a "Black Lives Matter" sign because some folks in the congregation care strongly and nobody terribly strongly objects to it; that doesn't mean that they're being coerced by the outside. Literally the SCP Wiki changed its logo to have a rainbow flag and there were all the same discussions about whether it's performative and unnecessary, and that's just a bunch of folks on the internet writing fiction. So I don't think this behavior is unique to corporations being profit-seeking or someone coercing corporations in particular.

(The part that seems unique to corporations here is the inability of corporations to espouse progressive goals that do negatively impact their bottom line, but... it seems obvious that this would happen.)