I agree that dark mode as an additional UI shouldn't be an afterthought, and should be tested fully just like the main UI. Poorly-designed dark mode can be difficult to use because of things like bad contrast.
Dark mode usually has lower contrast ratio (gray-on-gray text instead of black-on-white), and that's definitely proven to be harder to read.
The beyond-frustrating thing for me is that Windows 3.1 supported dark mode via system color palettes along with any other color customization anyone wanted to make to their entire system in a single place. Now every single application is custom-drawn and custom-themed, so these sorts of customizations are impossible.
This all worked better literally 30 years ago.
Also even light mode is often gray on gray, with backgrounds like #eee and text like #112 for example. The contrast is probably lower on average for dark mode, but it can still be designed well.
I don't understand this. Do people not use lamp or light source in their house? Are people living like cavemen? Otherwise, how is it that much difference between day and night+lamp?
If it is sleep time, there is already blue light filter most OS supports nowadays. No need to ask each app to support a separate color scheme.
Besides, you don't stare straight at your lamps. You do stare straight at your screen. The "night mode" just kills all color on your devices. It's a lot worse option than dark mode.