Avoid default fullscreen (no header, no dock)

I don't think there is any way to change the default behaviour, but you can return to the older Maximise functionality by Opt ⌥ clicking the green dot.

This will not always fill the entire screen, but has the old switchable behaviour that you might be used to, first click enlarges, second click returns to last state.

This older functionality is still also available in the Dock prefs - Double-click a window's title bar to… zoom
This is the same as Opt ⌥ green dot.

If you do want to completely fill the screen without being actually 'fullscreen' then Opt ⌥ double-clicking any corner of the window, when you see the diagonal arrows appear on hover, will expand to completely fill the screen - but it will not return on a second click & will also sometimes 'forget' the last size if you Opt ⌥ click the green dot afterwards.