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…