I haven't watched it in a while, granted. Outside of Aangs pacifism, the resolution of which is, I would agree, very lib and one of the weaker parts of the show, I don't recall anything particularly lib. I think it's one of those works where the political messaging in vague enough you could read a variety of interpretations into it.

Honestly I think this need to label all media either "leftist" or "lib" or what have you, is a weird and time wasting obsession of people these days. Yes there's blatant examples of each, Legends of Korra for example is undeniably Lib, but in between those there's a sea of stuff that's open enough for there to be alternative readings. Plus while you can do political analysis of all media, that doesn't mean all media had explicate political messaging.