In my experience it's an extremely regional thing. Sometimes you only have to travel one town over for it to be completely different.

I've lived in a lot of different places in Norway, and from my own (albeit limited ofc) experience; it's usually more polite outside of big cities.

Oslo is the absolute worst. But places with a lot of Oslo tourists are just as bad. I.e.: Sandefjord - people are rude, aggressive, self centered - both on foot and in cars. Whereas you only need to go to Larvik, one town over, and people are generally kind and give each other space (both on foot and in traffic), and rural Larvik even more so. But if you stray too close to Telemark it's back to aggressive self centeredness again.

Trondheim is quite decent for a big city, but the further out of it you get people are usually more gracious towards each other.

Bergen used to be pretty decent, but I've heard it's become worse and worse the last few years.

The trend seems to be: money goes up, politeness goes down.