Denmark, Finland, Iceland, Norway and Sweden. None of these nations have an minimim hourly wage enshrined in law. Instead many of the base terms of employment, including wages, are decided via collective bargaining between sector trade unions and representatives of public sector and business interest organizations.
I live in Sweden by the way, so feel free to ask me questions on the topic and I’ll do my best to answer.
At least for Norway, this is not technically true, but it also doesn’t matter.
Unions will run surveys across their members every year, and as long as they have enough members to have bargaining power, they also have the data. So they don’t really need all wages to be public in order to negotiate.
What is public in Norway, is the total taxable income of individuals. This is meant as a measure against tax fraud, and also an annual source of entertainment as you look up local and national rankings of who paid the most taxes, check that you’re still making more than your middle school bully, and so forth. But total taxable income can contain more than wages, so that is not really the number you’re referring to, and as mentioned the union has better data anyway.