It can and should be done, but it’s quite a lot of work to do. This article concentrates on the natural light issue, which is a big one. But there are also ways that plumbing and fire protection are different in commercial buildings and residential. And there are probably other concerns besides that.

In some cases it may work out easier to demolish the building and put up an entirely fresh apartment building.

And real housing, not Musks “bunkbeds at the office” interpretation.