Hot dogs/weiners/frankfurters are German in origin.
Hamburger is also German. Yes, the “hamburger sandwich” (the hamburger served on bread) is American, but at its core…. the ground beef …. is originally a German concept.
Pizza is originally from Naples, Italy.
How about potato chips? Not a “dish” per se, but a national food. Maybe it would be the national snack. It is a 100% American creation from Saratoga Springs, NY. Potato chips are everywhere in the USA, eaten by almost every American, and not super common in other countries.