The best advice will be "you can catch anything almost everywhere".
The huge advantage you don't need a license for sea fishing, but of course have to follow the local rules.
So one day in Geirangerfjord there were guys fishing for 4 hours with motor boats and got nothing. I caught these two from 2 first deep casts from my canoe 5 mins from camp.
Then tourists are saying there is no fishing in South Norway. But one day I've got these right from the shore of the camp in Kristiansand. It was insanely huge school of mackerel that got stuck in that Isefjærfjorden due to the tide change.
We actually got twice shown on this image and had to start releasing catch. My wife was angry she'll have to clean all that fish
It was like each cast near the shore getting you a bite.
Again Sognefjord isn't considered good for fishing. It has over a kilometer depth in some places.
But still managed to get this over a meter long beast there
but took 4 hours of fishing.
I've read that best fishing is in Western and Northern Norway. We still plan to go to Lofoten, which is considered one of the best places to visit and fish.
But again you might get no fish in most advertised spots and get a ton in those considered bad
So again you can seafish in Norway almost anywhere. Just get the basics when the fish is more active during tide changes. Lots of fish might be even near the ports or bridges.
P.S. I love eating fish way more than meat so these trips are a great fun.