Must applicants for US citizenship surrender their foreign passport upon becoming naturalized?

Not the same situation, but Greenland left the EC in 1985 and it’s citizens are citizens of the EU by treaty.

I checked with my friend. Her Italian citizenship is “suspended”. It isn’t clear what that means, but she doesn’t hold Italian citizenship any more. She can re-activate if she wants to though. I think that is the key. Some countries always allow their birth citizens access to citizenship no matter what. Even though for practical reasons individuals give up the citizenship.

Apparently this is a much bigger deal in France than in Sweden.