I’ll attempt a steelman and say, no, employees are not doing deep work from 9–5, but I could see being in an office 9–5 setting the stage for a lot of deep work to be done. Moonlighting for another company I could especially see as detrimental to focus at work.

The nature of modern offices pretty much prevents deep work.

You're not going to get deep work when you pack people like sardines into neat rows of desks, where pretty much at any time someone within one row away is going to be in a meeting - conducted of course over teleconferencing software. Or some people will talk (honestly, being in the office mostly translated to chit-chat for me).