I did read “the conquest of bread”, but wasnt convinced at all by its suggestion that people would just spontaneously organise themselves one day, without any planning or preparation at all. And I dont see Engels as “justifying” authority, rather, authority is simply something that exists in objective reality, whether you like it or not.

It is true that there are forms of authority which need to be fought against, such as the authority of the boss over the worker, or bourgeosie over the working class. But a certain form of authority is necessary to wage a revolution, because there will always be a bourgeous minority who opposes it.