Your eyes become less sensitive to flickering in low light. That's how movie theaters could work at 24fps.
That's not to say no one can be bothered by it. But it's much less likely to bother anyone. I have sensitive eyes and tend to notice flickering at anything less than ~70hz. My Xs hasn't bothered me and I tend to use very low brightness even in well lit env.
Traditionally, movie theaters showed each analog film frame two or three times, so the flicker would be 48Hz or 72Hz, not 24Hz. 24Hz flicker is very obvious and annoying to everybody. Digital projectors might sample-and-hold like LCD displays and therefore have no flicker despite the low framerate.
That's not to say no one can be bothered by it. But it's much less likely to bother anyone. I have sensitive eyes and tend to notice flickering at anything less than ~70hz. My Xs hasn't bothered me and I tend to use very low brightness even in well lit env.