Yes, it is completely independent of f.lux. I spoke with 2 AppleCare Representatives and neither had even heard of the issue before.Does your solution work (while flux is running) for your external monitor? I am in a very similar situation to you. You can still adjust the brightness using Settings Displays Brightness. Since upgrading to High Sierra Mac OS 10.13.2 I have not been able to adjust the screen brightness or volume via my MacBook Pro Retina 15-inch Mid 2014's keyboard.

It is must to adjust display brightness according to. If you set it automatically, Mac will automatically adjust brightness based on the lighting in the room. Mac OS gives you option to change your screen brightness automatically or manually. The display show built-in display with black monitor image but i cannot find any setting or option to adjust brightness. Cannot Adjust Brightness On my Laptop( Mac os Sierra 10.12.2) Thread starter Dell94 Start date Mar 5, 2017. High Sierra Desktop Support High Sierra Desktop Guides. Learn the recipe for Adjust Mac Display Brightness from bottom given steps. You can change Apple MacBook Air, Pro Brightness, using three methods either remotely, using function key or manually.

But, you didn’t know the real way to set/ Adjust Mac Display Brightness on MacOS High Sierra (10.13.2) or other. Then select a scaled resolution option for the second display. Press the Option key while you click Scaled to see additional resolutions for the second display. After the display is connected, choose Apple menu System Preferences, click Displays, then click Display.

Adjust brightness mac pro manually