Argentina can run the printing presses to buy dollars. They will devalue their currency by doing so.
Argentina cannot guarantee to print enough Argentine pesos to settle its debts, because those debts aren't denominated in Argentine pesos. Somebody has to actually buy Argentine pesos for US dollars from the government, and they aren't going to just buy as many pesos as the Argentine government can print; what would be the point in owning practically all of the Argentine pesos in existence?
If they owe $123, that will currently cost 1000 pesos, but if they print 1000 pesos then the exchange rate can drop, and they can't buy as many dollars as they like just by printing more pesos. Suppose they only have 500 pesos, but they print 500 more, and now maybe it costs almost 2000 pesos to buy $123. They print another 1000, but now $123 costs almost 4000 pesos... there is potentially no limit, it depends on the Argentine economy being able to provide enough goods and services to be bought with pesos, so that people will still want to buy pesos for dollars, even if more pesos are printed.
By contrast, the US government
can guarantee printing enough US dollars to settle its debts, because those debts are denominated in US dollars, so the printing has no effect on how many dollars are needed to settle them.