Whether you can enter Norway depends on whether you are vaccinated or not and from where/how you travel to Norway. You can check on https://www.regjeringen.no/en/topics/koronavirus-covid-19/travel-to-norway/id2791503/.

Regarding the train from Stockholm to Narvik: unfortunately, there aren’t any cross-border trains from Sweden to Norway due to restrictions by the Norwegian authorities. Trains end at the last station on the Swedish side of border (Riksgränsen).

So can I enter in Norway with ferry or bus? This restrictions are valid only for the trains? Thank you

Yeah Norway is open for Tourist because of no reason they havent reinstalled the train connections :/ 

You can take ferries from Denmark or Germany or ofcourse Buses :)