The only way in which communism is inherently authoritarian is in that wealth must be forcibly taken from capitalists and landowners in order to help the masses.

When wealth was taken from capitalists and landowners in the Soviet Union, it results in millions of poor people starving to death. (the rich people were worked to death; the poor people starved to death; there was a lot of death)

And yes, that is a very significant way of being authoritarian. Taking people’s property to redistribute is about as authoritarian as it gets.