> Compulsory voting is an instrument to build authoritarianism, not to prevent it.

On what basis does someone make this claim? Authoritarianism is a broad stroke. Most of the time, they eliminate voting, not make it compulsory.

Classically, an authoritarian power only care about voting to initially take hold of power. Every attempt to coerce voting (one way or the other) after that is performative, not instrumental.