I love it when people post studies just because it agrees with their worldview. For full disclosure, I support the 4 day week but I know to be objective. None of those links contain references to proper RCT with control groups or a variety of office roles so there is really no evidence for it. Trial plus survey is a better term as it carries no scientific connotations.

You are not really going to get your average companies to participate in those kind of studies anyway. Those companies want warm bodies and it has nothing to do with empirical evidence