Spinoza's idea of passions as opposed ot actions is the essence of Marxist "alienation".
The issue of alienation is not merely feeling bad about labor feeling arbitrary, it's that the worker becomes a passive receptacvle of cause and effect and in becoming so literally has their capacity for generating contingnecy (that is, their own Free Will in the most metaphysical sense of the term) confiscated.
Abstracted labor-power is not a conceivable concept without some medium by which people are forced to do tasks rote enough to be quantifiable in a way that makes them fungible. The labor theory of value certainly isn't true in some ahistorical a-priori sense, nor is it merely an axiom of theoretical equilbirium economics: it's an idea that locally applies to conditions in which a worker's finite time and caloric energy is type-coerced into being a liquid asset (i.le. a commodity) by the mediating system.
When the properitor gets labor from people while exclusively retaining the accumulation of knowledge, tha'ts what enables a compounding accumulation of relative power. "Knowledge" in the monist sense is therefore generalizable to "Capital".
The labor theory of value as well as the more generalized equilibrium model of economics completely obscures this by ignoring the path dependent compound interest of infrastructure and expertise.
In many ways, alienation is simply the intuitive sense that you're exhausting your resources without further developing, like going to the gym and not gaining muscle; being demoted from organism to battery.