I could never tell if people who were claiming seeing more than the 24 Hz/FPS thing were serious or just excusing poor game optimization. They were either fanboys defending a poor job of a product, or simply had terrible eyes. But I think even with the latter you'd still be able to tell the difference in smoothness.

It's one of those things that once you experience a higher framerate in games it's very hard to go back to a lower setting.

I find it hard to get used to in movies/shows though. My TV has an option to insert frames for smoother playback to make it appear a higher Hz, but it often looks unnatural. It was hard getting used to The Hobbit movie (I think it was Desolation of Smaug) that was in 48 FPS. And Avatar: Way of Water was constantly switching between lower and higher frames for regular and action scenes, it was such a jarring experience.

24hz is the lower limit. People will perceive 24hz as a smooth sequence, especially with motion blur, while anything below it will start to look choppy. Of course humans can perceive higher frequencies. But 24hz became the standard because celluloid film is expensive especially in the early days of cinema. The less frames you need to shoot the less film you need to buy and develop. And film back then was probably not sensitive enough for the lower exposure times that come with higher frame rates.

I think it's the limit for what most people can see as jittery motion. You may be able to differentiate between higher FPS settings, but above 24 hertz most people shouldn't be able to see discrete steps.

That's at least how I've come to understand it