#Iceland tested a reduced workweek 2014-2019:

”A pair of trials covering 1.3 per cent of the Icelandic workforce revealed that slashing weekly hours led to better employee #wellbeing, with less stress and burnout, while #productivity stayed the same or improved. The positive results sparked union pressure in Iceland, and now 86% of Icelandic workers either work shorter weeks or have the right to ask to do so.“

https://www.theguardian.com/commentisfree/2024/nov/21/iceland-36-hour-working-week-stress-job

Edit: The initial source was misleading, so I replaced it and adjusted the quote. Also see: https://en.m.wikipedia.org/wiki/Four-day_workweek#Iceland