>Tax declarations are public information there and you can find out the salary of anyone pretty easily.

This true of almost all of the Nordics. For example, you can perform the same request from Skatteverket in Sweden.

>IMHO that kind of transparency is actually a good thing to have and helps prevent unfair practices where (e.g.: men get more than women or nepotism gets you access to better salaries).

This isn't implicitly true. If it were, Iceland wouldn't have had to pass a law to make unfair salaries (based on gender[0]) illegal.

[0] - https://www.businessinsider.com/iceland-gender-pay-gap-law-2...