The problem is that most sites implement dark mode wrong with too much contrast. It doesn’t work if you make it “black”. It’s more about dimming the lights.
Reading dark pages will never be as good as reading in a well lit room. But there are ways to make it work.
I have nothing against dark mode in principle, but please don't make it the default. Respect the user's preference.
Or, at the very least, don't use white on black. Soften the contrast so that, if you force me to read it, it's not burned into my vision.