MacBooks do not recognize external monitors are usually caused by connection, setup, or compatibility issues, rather than hardware corruption. 1. Check whether the cable is intact and whether the interface is tight, and confirm that the monitor power and input source are correct; 2. Try to restart the system, reset the display settings or use safe mode to troubleshoot software conflicts; 3. Adjust the resolution/refresh rate or update the monitor firmware to improve compatibility; 4. Further troubleshoot through third-party tools, terminal commands or create a new user account; 5. If the above steps are invalid, it is recommended to detect the monitor itself or contact professional repairs.

It's really a headache to not recognize external monitors on your MacBook, especially when you need to expand your workspace or presentate content. This situation is usually not caused by a broken hardware, but by a connection, setup or system problem. Let me talk about this problem from two aspects: common reasons and solutions.

Check whether the physical connection is normal

Many times the problem lies in the connection method, not in the device itself. First confirm the following points:

• Is the cable intact : Is the HDMI, USB-C or Thunderbolt cable damaged? Try changing a wire to see.
• Is the interface well plugged in : Some USB-C interfaces may also have poor contact if they are not plugged in deep.
• Is the monitor power and input source correct : Make sure the monitor is powered on and the correct signal source (such as HDMI1, DP2, etc.) is selected.
• Use original or certified wires : especially Thunderbolt 4 or DisplayPort Alt Mode-enabled wires, non-standard wires may not support video transmission.

If you are using a multi-screen dock, you can try connecting the monitor directly to see if it can be recognized.

Try restarting and resetting display settings

Sometimes macOS graphics service may have minor failures, and restarting the system is the easiest way to try.

If it still doesn't work after restarting, you can try refreshing the display information manually:

1. Press and hold Option Command Esc to open the Force Exit interface and select Window Server or Finder to restart.
2. Use the shortcut key Command F1 to force the mirror/extended mode to switch.
3. Go to System Settings > Monitors, press and hold Option and click Detect Monitors, and then click Use to view as list.

You can also try booting in safe mode to see if the monitor can be identified, which will help determine whether it is a third-party driver or software conflict.

Check Mac and monitor compatibility

Not all monitors fit perfectly with a Mac, especially when using some older models or non-standard resolution monitors.

• Is the resolution and refresh rate too high : Some monitors may not automatically recognize the Mac at high resolution (such as 4K@60Hz). You can turn down the settings in the monitor menu and try again.
• Whether firmware updates are required : Some monitor manufacturers will release firmware updates to fix compatibility issues.
• Mac graphics card support capabilities : For example, the number and specifications of external monitors supported by the M1/M2 chip are limited, so please check the official documentation.

Further operation suggestions

If you have tried the above method but it is not working, you can consider the following directions:

• Use third-party tools such as SwitchResX to manually add resolution configurations.
• Run the command sudo killall -HUP WindowServer to refresh the display service in the terminal.
• Create a new user account to test whether the system preferences file is corrupted.
• Finally, try connecting another computer to see if the monitor is normal and troubleshooting the monitor itself.

Basically these steps are the investigation. In most cases, the problem can be solved by checking the cable, restarting, and adjusting the settings. If you have tried all but still didn't respond, it may be a hardware problem. It is recommended to contact Apple support or professional repair staff for a look.

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