> Windows 95 didn't need a special 'dark mode' supported by the OS, because you just changed your colors in the GUI tool for changing colors and fonts and you were done.

You're over-romanticizing the past. There were plenty of apps even in the Windows 95 era that drew their own widgets and only half-respected the colors you set in the control panel, and that consequently looked like pureed ass if you changed the colors from the default.