> Do you have any evidence that this is the case for everyone at every company no matter what?

Of course not, you are asking for the impossible.

But we have evidences that 4 day weeks boost productivity at least in some settings. If you are interested in the topic, look up "4 day week productivity" on a web search engine, or "4 day week" / "4 day workweek" on HN [1,2] if you want previous discussions about this. The topic is not new here. You'll find many posts where companies think it works.

[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...