What Diap said
the middle button will be a pair of stacked (slight offset) IF you are Maximized
This has not changed since W3.x, just the styling (eye candy) rendering of these controls. Some 'daughter'/dialogs frames do NOT have resize controls.
Some of the controls also appeared (right click) on the taskbar icon PRIOR to W10

. was a great way to get qa lost over the side frame back (using the keyboard arrows)