I use fullscreen pretty frequently on laptops with certain apps. For instance, right now Mailplane is open fullscreen in one virtual desktop, and Slack is open fullscreen in another. While I sometimes feel like I'm an outlier, when I joked on Twitter about being the only person who used fullscreen, I got a surprising amount of replies from people saying "wait, is that uncommon? I use it all the time."

Actually, I frequently had Slack and Mailplane open in the "split pane full screen" mode on my 27" monitor at work back when going into the office was a thing, so it's not just a laptop thing, either.

I use fullscreen fairy frequently (or the sister functionality: split-pane). I also like the classic zoom functionality (which tries to intelligently size the window based on content).

The Windows "maximize" functionality is something I almost never use, on any platform.