Alienation: Companies, not the users, own the platforms and the created profit.
Appropriation: Users spend time on corporate Internet platforms that are funded by targeted advertising capital accumulation models. The time spent on corporate platforms is the value created by their unpaid digital labour. [...]
the last part means that all surplus value is appropriated
he says later (p263):
One hundred per cent of their labour time is surplus labour time, which allows capitalists to generate extra surplus value and extra profits.