Target Display Mode not working?
What actually still works in 2026.

Why is Target Display Mode not working?

Target Display Mode lets an iMac show another Mac's screen over a cable. You press Command-F2 on the iMac, and it becomes a monitor. When nothing happens, it is almost always one of five things.

1. The other Mac is too new.Apple requires a Mac introduced in 2019 or earlier, on Catalina 10.15.8 or earlier. That rules out every Mac with Apple silicon, every Mac from 2020 on, and an older Intel Mac updated past Catalina.
2. The iMac's macOS is too new.The iMac must run High Sierra 10.13.6 or earlier. A 2012 or 2013 iMac updated to Mojave or Catalina has lost it, even with the same hardware.
3. The iMac isn't on Apple's list.The 21.5-inch iMacs from 2009 and 2010 never had it. Neither did any Retina 5K iMac, or any iMac after the 21.5-inch Mid 2014.
4. The cable or adapter is wrong.A 2009 or 2010 iMac needs Mini DisplayPort. A 2011 to Mid 2014 iMac needs a Thunderbolt or Thunderbolt 2 cable. Docks and hubs generally don't pass the signal.
5. The keyboard doesn't send the shortcut.If the function keys are set as standard keys, press Command-Fn-F2. Some third-party and older Apple keyboards don't send it at all.

Check your setup in one minute

All three rows must match. These are Apple's own rules.

The model and macOS of each Mac are under Apple menu, About This Mac.

One more trap: Mini DisplayPort and Thunderbolt ports look identical. Macworld warns that they are wired differently, and to look for the lightning-bolt icon on a Thunderbolt cable. And Plugable, a dock maker, says its docks and adapters don't pass Target Display Mode. The two Macs need a direct cable.

If your setup qualifies: how to make Command-F2 work

1. Connect the two Macs directly.Use the cable from the table above, with no dock in between.
2. Log in on the other Mac.Apple's steps say to be logged in on the Mac that connects.
3. Press Command-F2 on the iMac.Or Command-Fn-F2 if the function keys are standard keys.
4. Still nothing?Apple suggests restarting both Macs, or logging out of the iMac and trying from the login window. It also suggests the keyboard that came with the iMac.

When it works, it is the most direct route there is. The iMac simply shows the other Mac's signal, for free. If your Macs qualify, use it.

Does Target Display Mode work with an M1, M2, M3 or M4 Mac?

No, according to Apple. The rule on the connecting Mac excludes every Mac with Apple silicon, whatever the iMac.

People have tried anyway. In a 2020 MacRumors thread, someone connected an M1 Mac mini to a 2011 iMac with Apple's adapter. The result: "Nothing Happened". In an Apple Community thread from the same month, an M1 MacBook Air used a Mini DisplayPort cable. The iMac's screen went black for 3 seconds, then came back. Treat it as unsupported, and don't buy cables for it.

What still works in 2026

With a Mac from 2020 or later, three routes are left. Each has its own limits.

• Software over a cable or Wi-Fi. Encore works with every Intel iMac from Late 2009 to 2020, and 2007 to Early 2009 with Encore Receiver Legacy. Your Mac needs macOS 14 or later. Other apps cover parts of that range: see the comparison pages.
• AirPlay to Mac. Built in, but only when the iMac is from 2019 or later and runs macOS 12 Monterey or later. Encore vs AirPlay to Mac covers it.
• Hardware. A capture card shows an HDMI signal in an app on the iMac. A display driver board replaces the iMac's insides and turns the panel into a plain monitor.

The full list, with prices and sources, is in Target Display Mode alternatives for Apple silicon.

What you give up without Target Display Mode

Software can't match a direct cable signal on every point. Here is what changes with Encore.

• Over a cable with at least 400 Mbps, you get a sharp, lossless picture. The cable guide says which cable fits your iMac.
• Over Wi-Fi, the picture is always lower quality than on a cable, especially off 5 GHz.
• Retina iMacs get sharp text at up to 2560 x 1440, scaled to the panel, not native 5K.
• Latency figures are not published yet.

You also gain a few things. The iMac works with any Mac on macOS 14 or later, over Wi-Fi or a cable. Its keyboard and mouse can control your Mac over a cable. And it becomes a clock and smart display when you stop. Apple's page says the other Mac can't use the iMac's camera or ports in Target Display Mode. With Encore, the camera and microphone are coming soon, over a cable.

Still stuck?

Look up your exact model on the compatibility page. Encore vs Target Display Mode puts both side by side. If you set up Encore and something doesn't connect, the troubleshooting page has a fix for each message.