There was the unreleased Windows “Blackcomb”, basically prior to Redmond seeing Apple’s Aqua, which was like a bit Windows 2000, a bit ME, flatness, outlines, square corners, and it could’ve been metro.

But resolutions and anti-aliasing were getting (slightly) better, so copy Apple, XP instead gets texture and rounds everything.

Vista was another interesting take, especially weird was the window controls. We are still living with those weird long controls with a margin below, but not above them, a lot of the time, even in flat land Windows 11.