Question about Xiaomi Mi Laser Projector 150"

Is it possible to adjust the brightness throughout the system? When I use the custom brightness setting in the settings, I can set it to 100 or 0 without the picture changing (brightness stays exactly the same). Only when I open an app like Netflix and start a film or series do I see that the brightness has been adjusted according to my settings. Why is that? Is it not possible to adjust the brightness everywhere?