I’m embarrassed to say that I’ve been using Mac for years and still don’t know how to make an application fullscreen like Windows does. The green button hides the menu bar, and alt clicking the green buttom makes the app bigger but doesn’t fill the whole screen. Either I am stupid or Mac is bad at discoverability.
I switched from Win10 to macOS recently and had to search the web to find this, so discoverability is certainly an issue. I suppose Apple would rather you just fullscreen a window than maximise a la Windows.