Anyone experienced remembers that any 60Hz CRT is a flickering mess, especially computer monitors that used shorter-lived phosphors, and any old TV had terrible burn-in. That's why you want to reduce the amount of bright pixels on it. That's not a legibility thing.

A display is not a light bulb if you aren't specifically making it a light bulb against the poorly lit environment. There's no difference between reflected and emitted light, what you actually need is much better lighting in the room, so your display doesn't stand out when used on a brightness level that provides sufficient contrast (and just because working in a poorly lit room is unhealthy).

Moreover, a light scheme in a well-lit environment is less eye-straining, because your pupils contract and adapt to the light. If you're using a dark display against a dark background, your eyes adapt to the dark and then you're hit with the bright text. If you want to display more than just text, dark mode becomes a problem because most of the content (e.g. pictures, videos) is not largely dark.

tl;dr avoid excessive contrast and flickering. Everything else is individual eyesight differences, opinions, and snake oil.