The Federal Statistical Office of Switzerland sends compulsory salary surveys to the enterprises itself. The collected data is then published in the Salarium [1].
It is based on more than 750'000 salaries from the private sector and runs since 1994. You can read more about the methodology in the PDF [2]
I worked as a Software Developer for a company that used the data as base for their salary negotiations and it worked quite well.
There was no "hence salary" part. The salary back-estimation was very rough, e.g. for my income the estimation by a popular calculator was off by 25%. Using past tense here because anonymous access to tax data is discontinued.
You could tell if someone was poor or rich based on that, but for comparing incomes in your cohort it was not very useful.
https://www.youtube.com/watch?v=1bO8zEaSuWg