By the time of Frozen (mid 1800s), Norway, Sweden, and Denmark had been established nations/monarchies for many centuries.
Long gone is the time of independent monarchical city-states such as Arendelle seems to be. The three great powers were constantly vying to ultimate Scandinavian dominance for centuries prior and no small city-state would have been able to survive as an independent realm.
So, Frozen must exist in some alternate timeline in which Norway is still comprised of many city-state monarchies and hadn't been united centuries earlier, OR, it's some city-state/monarchy that held out from being assimilated into either Norway, Sweden, or Denmark for half a millennium. And even if it was a separate city-state and not part of a Norwegian government, it's still clear it sits on the Norwegian coast.
It is super-clear to everyone that this is an alternate timeline and Arendelle is a city-state monarchy located in Norway... except by those who hate the IP being added to the Norway Pavilion, who suddenly start taking issue with actual real-world geography and history in a movie with magical ice powers. Magical ice powers and real-world history normally don't co-exist with each other.
It's Norway. The film makers have said so. The cookie in the shape of Norway was a nose-tweak to Norway-deniers. Norway tourism board sponsors Frozen trips.
Only EPCOT purists refuse to believe Arendelle is set in Norway.