With a centralized ledger. You don't have to smuggle dollars in any more than you have to smuggle stablecoins in.

What centralized US-dollar-denominated ledger does an Argentinian citizen have access to?

What Bitcoin exchange does an Argentinian citizen have access to if Bitcoin exchanges are banned? It's the same thing. You just have to know somebody willing to act as a bank outside Argentina, just like you would have to know someone who is willing to break the law to sell Bitcoin to you.

I still don’t see what that has to do with the ability of an Argentinian resident to hold and transact in US dollars.

In exactly the same way that they hold and transact in Bitcoins.