Blog posts, articles, books, etc (basically everything that has more than a few sentences to consume): light mode the majority of the time. I have difficulties reading big chunks of text on a dark background no matter the contrast.
Except when I'm having a bad headache, then dark mode for everything (where it's convenient to switch) cause the light makes it worse.
Things like Twitter (short sentences, lots of input, usually on my phone), almost always dark mode by default.
If I'm reading in bed with the lights off, often dark mode too so the light doesn't wake up my fiancée.
On my phone I don't bother to switch from the default a lot of the time because the toggles aren't always easy to find and I don't have patience.
This 👆
Examples:
I agree it comes down to the preference and context.