Spam musubi is identical to your pumpkin pie example, main ingredient changed and often with different sauces/sides/etc like spicy mayo, teriyaki or gravy. Either they’re both unique or neither one is and, based on how you categorized everything else, nothing is unique.

Loco Moco is just egg curry with hamburger.

Gumbo is just bouillabaisse over rice.

Bolognese sauce on the other hand is, as I can’t find any other similar dish that was invented independently

Tomato based meat sauce? That’s just curry with some of the complexity removed.

Poutine nachos? Authentic Mexican food!

Also, think about what it means when you dismiss a food as “uniquely American” because it’s “Native American” cuisine.

Midwest and Alaskan, as well as east-coast, those three sound most promising. Can you maybe tell a bit more about them?

I’m sorry to say, but there’s nothing unique in any of those places either. Ambrosia is a standard fruit salad, Cincinnati chili is just spaghetti and hot dish is just shepherds pie. Sloppy Joes are just a ragú curry sandwich and corn dogs are tamales on a stick. Akutaq is just ice cream with an extra ingredient or two and birch syrup is “an ingredient, not a dish”.

This comment is an example of how that process continues. The original colonizers did their damnedest to try and erase those cultural lines and draw over them with their own.

Those cultural lines are faint, and per capita extremely weak, but that’s why it’s important to amplify them and highlight them when and where they exist instead of disregarding, ignoring and blurring them further.

It depends on how you define “uniquely created in the USA”.

Frybread has a rich and complex history within the USA, and I would argue it’s very much “uniquely created in the USA” but most variations have a pretty much identical recipe to hungarian lángos.

Also a lot of USA food is very regional. Hawaii has a lot of unique foods, such as loco moco, spam musubi, etc. but would be unrecognizable to most USAians.

Teriyaki dishes are technically Japanese, but the Pacific northwest has taken the concept and run with it to the point where it’s now it’s own unique creation. It also has cheese zombies, jojos, Seattle dog, huckleberry everything, etc.

Southwest USA and Mexican have a lot of overlap but are also just as distinct with “Tex-mex” being it’s own culinary thing. Puffy tacos, chili con queso, cornbread, cowboy caviar, nachos, etc.

Midwest, Alaskan, southern, east-coast, Puerto Rican, etc. all also have their own unique culinary traditions at this point with lots of micro-regional distinctions within them.

However, they aren’t marketed, advertised or popularized in the same way that things like “Chinese food” is. Despite “American-Chinese food”, like general Tsao, or orange chicken, being very much it’s own genre that is unrecognizable as either traditional/old recipe USA or Chinese foods.

To discover many of these things you can’t just “tourism” through but have to actually try to know and understand the people and places.

Conversely, it’s not like Italian food stops being Italian due to its use of “new world” food stuffs like tomatoes, or pasta is any less “Italian” despite it just being Chinese noodles with a few changed ingredients.

If you insist on playing that game you’ll find nothing is unique.