I'd be tempted to try the 12V-disconnect reboot-the-car trick. If problem is still there, it may be the rotary knob's malfunctioning somehow. It feels like a cheapo carbon-track variable-resistor potentiometer, so it ought to settle-down ok at several places in its travel, even if it's getting a bit worn and noisy. A noisy pot should make the screen brightness flicker a bit, but might be hard to spot this while driving over bumpy surfaces likely to provoke this.
It sounds to me your day light sensor is having a moment... it is not the dimmer switch.
If it is daylight and you switch on the lights the interior clusters will not go to "night mode" as it knows the light levels in the cabin, irrelevant with the lights being on .
When the car thinks it is sufficient lack of light... then it will switch the interior clusters to night mode and the dimmer switch works then.
So in conclusion the dimmer switch works when the car senses the lack of light and goes to "night mode"
Night mode is non existent .. jsut made it up to make things easier in a way lol
Hope it makes sense?
It is an intentional function of the car. All is normal! You'll get used to it. Annoying at first, but you can see the logic of it after a while.
"Yes, it does this and it is an intended function. If the sensor on the dash detects daylight then it delivers a fixed, very bright, non-adjustable light level to the dash. When it detects night time (which it often does during 'daylight hours' at this time of year due to low light levels) it will then change to the adjustable brightness level, which is adjusted on the roller button to the right. If you have that set to minimum AND it flips from day to night, then indeed it will drop from bright to "too dark" (IMHO). You have to make sure the dash light adjust fully up to avoid getting too big a jump in brightness level. Unfortunately, this is a direct consequence of all this 'new tech'. Where you have LCD screens only and no analogue needles, this sort f behaviour become a legally mandated requirement to ensure you can see vehicle speed in bright sunlight."
A lot more user-programmable features would have been good, but GM have been stung in the past by muppets doing stupid things with their cars, I can appreciate they make the car do what the law says, and that's yer lot!