Authoritarianism is at its core a far-right/fascist ideology, it can permeate left wing opinions but it is not left wing itself.
If a person or party or whatever calls themselves left wing and are in support of fascist ideas, they're not left wing despite what they say, that's confusionism, if you take it at face value you fall into their trap, you're both helping them and hurting left wing ideas, that looks like extreme centrism and it's not a good look