Tax relief is pretty much exactly the same as subsidies though. If the Norwegian govt didn't bother doing EV tax relief, they would get another x billion NOK in taxes sitting in the treasury. It's no different to giving the billions of NOK as a discount on the purchase price like other countries.
There is a huge difference. In one instance they government pays direct money to make something cheaper.
In the other they do not collect tax on something. The argument that the "could have had" the money is moot because they never had it in the first place like with subsidies.
It's like saying the US government is subsidising iphones since they could have had 100% sales tax on them but do not.
And lastly, the tax they collect on the ICE cars is a pollution and/or CO2 tax so it is not applicable to EVs anyway as they do not have an indirect cost to society in form of pollution. I think they should tax ICE cars even more and same with petrol and CO2 release in general.
Some municipals have free public charging stations but that's up to the locals to decide.