Infrastructure: Do homes have chargers, desks, screens? If not people will soon get carpal tunnel or lose productivity.
Internet/VPN security costs are real.
Productivity creep : Some of the main issues with WFH have been work hour creep. Managers and other employees feel its easier to make requests for more time given that you are now a few feet from your laptop. Lack of discipline also means that people now work longer.
Rewards and promotions I can't find it right now, but I recall WFH resulting in lower pay relative to people with the same qualifications who went to office.
Mental costs: One of the main issues with WFH has been loneliness. Fixing this requires immense effort to recreate physical proximity.
Creativity is also lost when you cant engage in banter and catching up with people.