Well, I'm not trying to take dark mode away from anybody. I assumed, the person I replied to did not have specific health issues, because surely, they would have mentioned them.
Of course, there's people who genuinely cannot leave the house without sunglasses, because of migraines or an eye operation or loads of other reasons.

I was mainly trying to say that it's not damaging to retinas, if you've got otherwise healthy eyes. Or at least the chance of light from a monitor, which has much reduced spectrum and strength than sunlight, being damaging in ways that sunlight is not, is extremely low.

Of course, the advantage of light themes, i.e. better readability in bright rooms (and bright rooms are generally better for mental health, when used during the day, due to stronger activation of circadian rhythm), that's also ultimately just a matter of comfort.
If looking at a dark theme even just brings you immense joy, then go for it.