It's obvious that this will only work in certain sectors and likely not suitable for anywhere where certain cover levels are required so shops, restaurants, nurseries, medical staff, emergency services, factory jobs, transport etc.
But I can see how it would work for office jobs where a lot of the productivity savings required to fit 5 days work into 4 can be made by dropping tasks that aren't strictly essential, reducing the time allowed for meetings, looking a what can be done more efficiently etc.
A lot of the time if you allow an hour for a meeting it will take an hour, if you allow 45 minutes, the same updates, decisions etc will take 45 minutes, with effective chairing.
Or drop some of the meetings. A lot of office workers talk about their jobs being 'back to back calls' where they only have to listen in and contribute to part of the meeting.
To me that seems incredibly inefficient and you can't do anything particularly useful that requires focus and concentration at the same so its not likely a good use of time.
Also if your workplace has the 'copy every email to all and sundry' culture which means you spend ages wading through emails. Half the time no-one is reading most of those emails and I think it's probably not the most efficient way of communicating.
My workplace is very bad at this but I'm thinking that there's likely a better way where you set up Teams channels or similar for a particular project, client or workstream and all discussions, documents etc live there.