My "office" is a converted deep (e.g. bedroom) cabinet, with a sliding keyboard tray and some shelves sawed out. My chair rolls in and fits within it, so the whole thing can be closed off when not in use. And that's because I want a large fixed screen. I think as people stay WFH, people will find ways of packing office spaces into smaller spaces. But people will also take advantage and move further out to get more space.
I know of some start ups where employees got paid local co-working spaces, so they can go to any nearby where they live if they don't have space at home or don't want to work at home, but don't want to commute. There are solutions in between.
My boss goes in to the office even on non-office days.
If I still lived in an apartment - ie, no separate room at the house to use as an office - I'd probably go in most days as well.