It was actually NeXTSTEP that introduced the familiar "Windows 9x" 3D control appearance and close buttons on the top right. The first versions were released around '88.
I love that interface. If I ever get a lodpi monitor again I'm going straight back to Windowmaker.
And the Windows 1.0 UI [1] looks really similar to Mac OS (especially dialogs and buttons), so apparently Microsoft pilfered their UI design from Steve Jobs's companies not only once but twice.
[1] https://www.pcjs.org/software/pcx86/sys/windows/1.00/