Is 21st century American culture and society "postmodern"? It seems to me that American culture and society accepts the core foundational principles of the "Enlightenment" and "Scientific Revolution." It has always been my understanding that American culture and society has never challenged the assumptions that have come out of those movements.
If American culture and society were, say, based on the philosophy of "Marxism," for example, then I would say that we are a postmodern society and culture, because Karl Marx was what is considered a "postmodern" thinker.
I would imagine that an actual "postmodern" society is a very hard thing to achieve. Even the Soviet Union, at the end of the day, was not a "postmodern" society, despite its alleged devotion to "socialism."
As for resemblance of present-day "Modern" American culture and society to Victorian-age England: I suppose it lies in the fact that the United States has perhaps the highest child poverty rate among all the other advanced industrial nations of the world.
Oh yeah, and we imprison numerically more and a greater percentage of our citizens---especially the black and brown folk---than any other country in the world; we're gloriously number one in that department. No doubt the prison also doubles as the "workhouses" of old.
Recall "The Christmas Carol" in which Scrooge, unsympathetic to the poor, says to the Spirit of Christmas Present, concerning the poor: "Are there no prisons? Are there no workhouses?"