What is Heated popup? (System UI & Settings)
If you adjust brightness when the device is heated to reach a certain temperature,
a pop up that says “Cannot brighten due to high temperature of phone.
Try again later” will appear, and brightness cannot be controlled.
Pop up does not appear as slider bar can be controlled.
However, there is a maximum temperature for a phone,
therefore the settings will be modified again even though you force to control brightness settings.
Home → Indicator Setting → Display → Brightness