Mac OS · macOS
Fix an external display that is not detected by Mac
Source-checked About 10 minutes
Answer
Check the display’s power, cable, adapter, and your Mac’s supported display count, then use Detect Displays in System Settings. A Mac cannot drive every number or type of external display, even when the cable fits.
Check the display path
Turn on the display and confirm it has the correct input selected. Reseat the cable at both ends and, when possible, test a known-good cable or a direct connection instead of changing display settings first.
Check Mac display support
Choose Apple menu > System Settings, select Help in the menu bar, then choose your Mac’s Specifications. Review Display Support or Video Support for the supported type and number of external displays.
Open Displays settings
Choose Apple menu > System Settings, then select Displays in the sidebar. Review the connected-display list before selecting a resolution, arrangement, or mirror option.
Use Detect Displays
Hold Option in Displays settings to reveal Detect Displays in place of Night Shift, then click Detect Displays. This asks macOS to look for the attached screen again.
Reconnect and wake the Mac
If it is still absent, disconnect and reconnect the display, put the Mac to sleep and wake it, then test the direct cable and correct adapter again.
Verify the configuration
When the display appears, choose mirror or extend as needed and verify the resolution and brightness. Test one restart only after the physical and support checks are recorded.
Video walkthrough
If it does not work
- If Detect Displays does not find it, compare the Mac’s documented display limit with the monitor, cable, adapter, and dock configuration.
- If another display works with the same Mac, focus next on the original display’s input, cable, adapter, or manufacturer instructions rather than resetting macOS.
Sources and verification
Checked against official documentation on . Scope: macOS.
Follow the linked first-party guidance if labels differ after a platform or app update.