Option-clicking the green button (usually) maximizes. Full screen in a separate desktop space may resemble maximizing in some ways, but it significantly changes the interaction model when switching between windows, especially when some of the windows are not maximized. Example:

1. Open two apps, at least one of which supporting fullscreen.

2. Open three windows in the app that supports fullscreen.

3. Fullscreen one window.

4. Cmd-tab to the other app.

5. Cmd-tab back to the previous app.

If your window from step 3 was maximized (filling the screen in the same desktop space), you would return to that window, but instead you are now looking at some completely random other window that you were not interacting with at all.

For people who cmd-tab (and cmd-`) frequently to switch between apps, this is super jarring and not at all what we intended to do.

I just double tap the titlebar

With years of muscle memory, I reverted this change back to its original behavior (double tap minimizes the window to the Dock).

In my experience, the green button would make things maximum tall, but not maximum wide. I did not have any extensions. As opposed to everywhere else where maximize makes the selected window fill the full amount of windowed area.

And I'm reminded by other posters that they changed it to full screening (which is also not maximizing), complete with a disorienting animation, ugh. Pretty happy being Mac free again.

The old way was called "zoom" and would make the window fit the content.

Yeah, but what does it really mean to "fit the content", if it doesn't fit the window at any size, but can reflow horizontally - as in e.g. most webpages? Mac apps seem to prefer increasing the vertical size until the window is as tall as it can be, but for horizontal, they usually stop before they reach full screen width - even if this would fit more content on the screen.

It's supposed to be "smart", in a sense that it gives you the largest window size that it considers usable. But that's too subjective an assessment to enable it by default, and even more so to not make it configurable at all.

It typically fullscreens apps for me. I think you can hold down option and press the green button for maximization.