America has always been slow to adopt changes to the work week. It wasn’t until the late 1920s that the idea of a shorter work week—from 6 to 5 days—gained widespread support. The 5-day 40-hour work week has been the norm in the U.S. since the Fair Labor Standards Act passed in 1940. For today’s businesses the 4-day week could be the logical next step towards work flexibility, where productivity and creativity are measured rather than the number of “face time” hours put in at a specific workplace location whether office or remote.
Source: https://hrtechcube.com/80-years-in-the-making-4-day-work-week/