What To KnowGo to System Preferences > Displays, click Scaled and hold down the Option key to show and select the Detect Displays button.Go to System Preferences > Displays and check the resolution and brightness settings.Also, check the display cable connections, and update adapter software if applicable.
This article offers tips on the display settings and cable specifications to check to fix an issue with a Mac not detecting an external display.
Check Your Display Preferences
Regardless of your MacBook Pro or other Mac model, it's not uncommon to experience a display connectivity issue when hooking up an external monitor. If you've hooked up an external display to your Mac and nothing is happening (just a blank or black screen appears), your display preferences are the first place to look.
Click the Apple icon in the upper left corner of your Mac's menu bar and select System Preferences.
From System Preferences, choose Displays.
In the Resolution section, select the radio button next to Scaled and then press and hold down the Option key. This combination will reveal a hidden Detect Displays option at the bottom right. Click this button so that your Mac can scan for a connected display.
Alternatively, you can put your Mac to sleep briefly and repeat the above steps. Click the Apple icon and select Sleep.
Wake it a few seconds later to see if that was enough to locate the display. If not, try again to force the Detect Displays scan.
The above steps can help nudge your Mac and external monitor to sync up or prompt your device to scan for and connect to an attached display. It could be helpful to unplug and replug the cords before trying this sequence.
Adjust Display Resolution Settings
Another possible reason your external display isn't detected (or you end up seeing a dreaded pink screen) could have to do with display resolution and brightness settings.
Go to System Preferences > Displays.
Next to Resolution, select the radio button next to Scaled and choose different resolutions other than the default option to see if this prompts a change.
Under Brightness, uncheck the box next to Automatically adjust brightness and manually brighten using the toggle. If the external display's brightness is too low to register, this could resolve that issue.
If you haven't already done so, another helpful nudge could come from plugging your computer in to its power adapter and avoid relying on battery power alone.
Double-Check Display Cable Connections
If your Mac still doesn't recognize your display after prompting the Detect Displays scan and adjusting resolution and brightness, it can help make sure connecting cables are in order.
First check to see that your cable is secure both to and from your monitor and your computer.
Even if the cable connections are secure, remove and reattach them to see if that makes a difference.
If possible, use the same cable with another port on your Mac.
If you don't have another available port or cable, try using it to connect to another Mac-compatible external display to determine if it's a cable issue.
If you're attempting to connect two external displays, know that not all Macs support more than one additional monitor. You can check the supported number of displays by clicking the Apple icon in the upper left corner of your Mac's menu bar and selecting About This Mac > Support > Specifications > Graphics and Video Support.
Make Sure You Have the Right Adapter
Depending on your particular Mac, chances are you'll find yourself working with third-party hubs, adapters, or display software to extend your display. Before using, it's important to check for compatibility with your particular model.
Make sure that your monitor and cable combo is compatible with your Mac. Some Macs use only USB-C or both Thunderbolt and USB-C connections, while some Thunderbolt variations require a Thunderbolt-specific adapter.
Since USB-C and Thunderbolt 3 ports look virtually identical, it's important to ensure you know the ports on your Mac and that any third-party USB-C or Thunderbolt adapters and cables are compatible.
If you're using a third-party connector or dock, make sure you've downloaded any relevant software or updates if applicable.
If you're not having luck with software updates, the hub itself could be the issue. Try a direct connection with an Apple Thunderbolt or other compatible cable to determine if that's the source of the problem.
Increase your chances for success by avoiding daisy-chaining several adapters and cables together. Macs tend to work best with external displays when an Apple-branded or compatible cable and adapter are directly involved.