A MacBook, or any type of Mac, can be used with an external/additional monitor. You don’t have to use an Apple manufactured/approved display but those will work best. If you have a non-Apple approved display, you will find that it works, just not as well as an internal display. If you’re using it as a secondary display, fewer features will work. Case in point; brightness. Brightness is a basic setting that users change on their displays. Some adjust it according to the time of day or the amount of light in the room. There are dedicated keys on an Apple keyboard for controlling brightness but they do not work on external displays. Here’s how you can control the brightness of external monitors on macOS, and get the dedicated brightness keys on an Apple keyboard to simultaneously change the brightness for all connected displays.
Brightness for displays
To control the brightness of external monitors, you need to install a free app called MonitorControl. Download the app and move it to the Applications folder. This app is going to work with the brightness keys on your Apple keyboard but in order to do so, it needs special accessibility permission.
Once you’ve granted the app permission from the System Preferences, it will run in the menu bar. You can click the app’s menu bar icon and use the slider to change the brightness for the external monitor. To use the brightness keys, make sure the external display is the active one and then tap the brightness keys to increase or decrease the brightness.
To change the brightness for other displays, simply click the display so that it’s the active one and use the usual brightness keys. You will see the macOS display control on the screen.
Right now, in its default state, the app doesn’t let you change the brightness for all displays at once. Instead, you have to manually switch over to the display you want to change the brightness for. To fix this, open the app’s preferences and go to the Display tab. Enable the ‘Change Brightness/Volume for all screens’ option. When you next tap the brightness keys on your keyboard, the brightness will change for all your displays at the same time. We should warn you that a Mac’s internal display’s brightness can be set to zero where it looks as though the screen is off. This normally doesn’t happen with other displays so be careful how low you set the brightness.
MonitorControl isn’t just for brightness. If your monitor has built-in audio output and the port that it’s connected to allows macOS to send audio to it, you can use the volume keys on the keyboard to control the volume for both the internal speakers as well as the monitor’s own speakers.