The less than 400k population is a good sample size, however, their main revenue comes from tourism, aluminum smelting, and fisheries, and they have a relatively large source of geothermal and hydropower with a very homogenous population (>80% Icelandic). Data centers are about 1% of its GDP. Even Iceland needs barkeeps and restaurant workers to work at least 5 days/week with restaurants in touristy areas open 7 days/week with shorter days on Sunday. Having worked a life of manual labor and white-collar jobs, sometimes both in the same job, the 4-day work week is really for specific types of industry or work. Tech, for sure, but not the food service industry...