I know that authoritarian is a lib-brained anti-communist term that one shouldn't use unironically. But what other term would you use to describe those who seems to have a love for the exercise of state violence and coercion for its own sake? The howling hogs who cheer when police beat up protesters, the psychos calling for refugees to be gunned down at the border, the monsters who revel in the misery of the poor and love to step on those who cannot defend themselves.
You could call them rightists or conservatives or something like that but that doesn't carry the appropriate stigma or convey the wickedness of their proclivities. You could also call them fascists which would be correct most of the time but it is too broad a term to center in on their specifically sadistic relationship with state power. It also plays into the liberal idea of fascism being defined by "fascist methods" instead of by fascist ideology and belies the existence of the well-mannered and polite fascists who are the most dangerous kind.
Among other socialists/leftists, some variation of reactionary or oppressor is fine. Most people would find common ground with it. The problem with using "Authoritarian" is that these people don't necessarily have a love for authority, just the kind that targets the "bad guys" while working for them (The Capitol "Insurrection" is just one out of many examples of hypocrisy on display).
With Libs, I consider "Authoritarian", just like Regime or the myriad other loaded words, perfectly fine to try to turn around and use against them, or Cons/Rightoids. On some level, appropriating lib terminology might be necessary to "speak their language" and maybe get a tiny few of them to introspect.