Let me restate the problem: I set my system-wide window background to black and text color to white. An app developer sets a label to dark gray text and default/transparent background. The end result is that I cannot read the label. Or the developer uses black icons on the toolbar — and I cannot use the toolbar, because I can’t see anything.
macOS introduced system-wide dark mode a few years ago, but app developers had to recompile and opt into it. This was done so that they could adjust their artwork and overridden colors to it. Windows 10 added dark mode, but only for "modern"/UWP apps. Classic Win32 apps need to implement their own dark mode with custom themes/controls (like Explorer does).