Why do stars twinkle?
This happens due to the influence of the atmosphere. It consists of various air currents with different temperatures, densities, and speeds. Light from a star passes through all these layers, and it doesn't come without a cost. One of the currents can strongly deflect a light ray, and as a result, an observer on Earth temporarily loses sight of it - the star "goes out", then this current changes and lets the light through in the right direction again - the star "lights up". This happens continuously, and we see twinkling.
It's also interesting that a star can not only change the intensity of its light, but also its color.
Let's say it emits pure white light, which already consists of all the colors of the rainbow. This light encounters a layer of atmosphere on its way that, for example, passes green rays well, but scatters and refracts the others. As a result, an observer on Earth will see the green color well, while the others will be weakened and almost invisible. And this lasts literally a fraction of a second.
As with brightness, different layers of the atmosphere will refract colors differently, and the star behind them will change its color. But our eyes are much more sensitive to changes in brightness than color, so we barely notice this kaleidoscope.
Beyond the atmosphere, stars shine steadily and don't twinkle. On the surface of other planets with different atmospheres, they may twinkle differently or not twinkle at all, for example on Mars, where the atmosphere is much less dense.