Verify how many displays the exact Mac supports, reconnect power and the cable, choose the correct display input, then use Displays settings to detect or arrange it. Test a direct compatible cable before a dock or adapter.
What this covers
- Supported Macs connected to an external display by USB-C, Thunderbolt, DisplayPort or HDMI
What it does not cover
- ×Display counts or resolutions beyond the Mac model’s specifications
Try in this order
0 of 4 completedCheck the Mac’s display specification
ReversibleLook up the exact Mac model’s supported number of displays, resolution and refresh rate before changing software.
Reconnect power, input and cable
ReversibleChoose the display’s correct input, reseat both cable ends and make sure powered docks have their adapters connected.
Test a direct connection
ReversibleBypass a dock or switch with a known-compatible cable or adapter connected directly to the Mac.
Open Displays settings
ReversibleUse System Settings › Displays to detect, arrange and choose a supported resolution after the hardware path is stable.
Evidence ledger
Sources behind this answer
Exact questions
Common questions about “Mac does not detect an external display”
Why does the Mac not see the display?+
The cable, adapter or port may be unsupported.
Should I check Displays settings?+
Hold Option and click Detect Displays.
Is the cable or adapter suitable?+
Not every USB-C adapter carries video. Check that it supports display output.
Should I use Detect Displays?+
Hold Option in Display settings to show it.
Would a restart help?+
Restart with the display connected.
Does the display need to be on the right input?+
Check the monitor's input source. If it is on another input, the Mac may detect nothing. Some monitors also need an option enabled for USB-C.
Would sleeping and waking the Mac help?+
Sometimes. Disconnect and reconnect the display after waking the Mac to trigger detection.
Should I try a different port on the Mac?+
Ports on the same Mac may differ in what they support. Try another port and cable to rule them out, and check that the display's input and any dock are set correctly.
Could a dock or hub limit the display?+
Docks and hubs share bandwidth among their ports and may not support every resolution. Connect the display directly to the Mac to test, then add the dock back.
Is it worth testing the same cable and display on another computer?+
Yes, and it settles the question fastest: if a different laptop detects the display fine over the same cable, the fault is isolated to the Mac's port or its display-output settings, while a display that still fails to show up on a different machine points at the cable, adapter or monitor instead.