There aren't many traditional dishes that are vegan. But some can easily be made vegan and be just as tasty! Kroppkakor is a potato dumpling, originally filled with pork. They're great filled with vegan fillings as well. Try a filling made with chanterelles, hazelnuts and herbs, served with finely grated carrots and lingon berries! Delicious!

I can only think of three Swedish dishes that are traditionally vegan without any modern adjustment.

1: Pea soup/Ärtsoppa. You take dry yellow peas and put them in water for the night. Then you boil them in water for a 1-2 hours to make the soup. Traditional spices are rosemary and mustard. Not too exciting but it's okay. Some add pork but it's also traditional to not add pork

2: Bruna bönor. Can't translate this one but it just means "brown beans" but Bruna bönor specifically refer to both a bean variety which is exclusively grown in Sweden and to the dish its most often made into. The dry beans are soaked in water for a few hours then boiled in a water and vinegar mix until they have been cooked broken. Think like an Indian dhal but without spices... Not too exciting but it can be okay. It's serves with potato. Was big with construction workers and other hard laborers in the early 1950s. Many add pork but it's not strictly needed.

3: Porridge cooked with water. Not too exciting. Part of Nordic cuisine but hardly exclusive to Nordic cuisine. Oat, rye, wheat semolina. Many versions are available but it's only a breakfast dish.

The traditional Nordic cuisine is not very vegan friendly...

A traditional dish in Denmark would be open sandwiches with various toppings. One of which is a fried fish filet, which can be easily made using parsnip instead. Try translating this recipe:

I usually make this to imitate the traditional Danish Christmas food:

Boil potatoes and carrots and use the stock to make a brown sauce: https://gastrofun.dk/opskrift/vegansk-brun-sovs/ (use Google Translate or similar)

You would have to make some kind of meat substitute. You can make a nutty pie or maybe some Seitan-based meat.

Serve with salty crisps (to dip into the brown sauce), pickled cucumber salad and red kale salad (either raw with oranges or cooked in vinegar and sugar. Maybe look up a recipe).

Also I tend to make some brown potatoes. Heat sugar in a pan, add lots of vegan butter and toss and turn the cooked potatoes into the mix.

Merry Christmas ;)

There are plenty veganised recipes for Köttbullar, if you want to take a stab at that.

There's some fun vegan pickled herring recipes out there with aubergine as the herring substitute.

Can't speak for Swedish or Norwegian cuisine, but I am having a hard time coming up with "traditional" Danish vegan dishes. Most of the vegetarian dishes I know of will at least use milk. But if plain, boiled, white potatoes is something for you, that would be as traditional as it gets.