"donc" is "therefore" (though shorter and less pompous).
In those contexts, "Donc" is more like, "Word!" or "Right on." I would translate those to mean, "Agreed."
Or is that just French that French teachers and textbooks talk about to students in America?
I think the meaning of "Agreed" or "Right on" is rare and more implicit. Like saying "therefore" might mean "I accept the premise".
As a question, "donc?", like "so?", can mean "and then?", "then what?", "meaning what?", "what next?" or "so what?"
As an interjection or at the beginning of a sentence, "donc", like "so", can mean "now then", "that said", "moving on" or "without further ado".
I basically never hear that as a standalone reply in English!
As an interjection or at the beginning of a sentence, "donc", like "so", can mean "now then", "that said", "moving on" or "without further ado".
I'm not sure, but I think sometimes when my wife is saying, "schma" it's somewhat like "donc" you describe above. But sometimes, I think she expressing agreement with a person that a third party was a bit mistaken or off the mark, so it's expressing a kind of disagreement. Not sure.