At least before you are grown up - that’s absolutely proven truth.
Until you are an adult - you must get outside light (even if it’s overcast winter). On average - luminosity (I hope that’s the term) outside is orders of magnitude above indoors, even when it’s overcast.
Kids without enough light have much bigger risk of shortsightedness. Because eyeball development is related to light.
There was even an article about this on HN couple weeks ago.
That depends entirely on what you're doing in that dim lighting. And how much time you spend in it. Spending all of your time in dim lighting is absolutely bad for your vision, or at least that is the contemporary consensus in optometry.
it is a myth that dim lighting negatively impacts eyesight long term.