How to connect Mac mini to iMac

Use your iMac as a display with target display mode - Apple Support

You can use the 2009 iMac as a display for the 2014 Mac mini if your setup can satisfy all of these conditions:

• The iMac is a 24" or 27" model. The 21.5" Late 2009 iMacs do not support Target Display Mode.
• The iMac is running macOS High Sierra, or earlier. It will be, since 2009 iMacs can't run anything later.
• The Mac mini is running Catalina or earlier. The Late 2014 Mac mini can run Big Sur and Monterey, but if you are running either of those versions of macOS, it won't support using the iMac as a Target Display.
• The connection is a Mini DisplayPort one. The Late 2014 Mac mini has Thunderbolt 2 ports which use the Mini DisplayPort connector, and a 2009 iMac would have a Mini DisplayPort. So the connection would consist of a Mini DisplayPort to Mini DisplayPort cable.

The requirement that "the other Mac" (the Mac mini) cannot be running anything later than Catalina is likely to be the killer here. I can't recommend downgrading from Monterey (still one of the "most recent three") to Catalina just to reuse an old 27" 2560x1440 or 24" 1920x1200 pixel screen.

The following older iMac models can be used as an external display when plugged into another older Mac model.

iMac models introduced in 2011, 2012, 2013, and mid 2014

To use any of these iMac models as an external display:

• The iMac used as a display must have macOS High Sierra or earlier installed.
• The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
• The cable connecting the two Mac computers must be a Thunderbolt or Thunderbolt 2 cable.

24-inch and 27-inch iMac models introduced in 2009 and 2010

To use any of these iMac models as an external display:

• The iMac used as a display must have macOS High Sierra or earlier installed.
• The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
• The cable connecting the two Mac computers must be a Mini DisplayPort cable.

How to use target display mode

1. Make sure that your iMac is started up and meets the system requirements above.
2. Make sure that the other Mac is started up and logged in to a macOS user account.
3. Connect the two computers using the appropriate Mini DisplayPort or Thunderbolt cable.
4. You can use more than one iMac as a display, if each iMac is using a Thunderbolt cable to connect directly to a Thunderbolt port on the other Mac (not the other iMac).
5. Press Command-F2 on the keyboard of the iMac. You should now see the desktop of the other Mac.
6. To exit target display mode, press Command-F2 again. Or disconnect the cable, or restart either Mac.

Apps that were open on your iMac when entering target display mode remain open in target display mode. For example, if you begin playing music on your iMac and then enter target display mode, the music doesn't pause on your iMac.

The other Mac can't use the iMac computer's built-in camera or ports. To use external devices with your other Mac, connect them directly to the other Mac, not to your iMac.

Control brightness and sound

If you want to use the built-in speakers of your iMac to play audio from the other Mac:

1. Choose Apple menu  > System Preferences, click Sound, then click Output.
2. Select the iMac as the device for sound output.

You can then use the sound and media keys on the keyboard of the other Mac to adjust volume and control media playback.

To control the brightness of the iMac display while it's in target display mode, use Displays preferences on the other Mac, or the brightness keys on the keyboard of the other Mac.

If target display mode doesn't work

If your iMac doesn't show the desktop of your other Mac, try these steps first:

1. Restart your iMac.
2. Restart the other Mac.
3. Unplug the Thunderbolt or Mini DisplayPort cable from the other Mac, then plug it back in.
4. Press Command-F2 on the iMac.

If that doesn't work, try these other solutions:

• If you're currently logged in to the iMac that you want to use as a display, choose Apple menu  > Log Out to return to the login window. Then press Command-F2 again.
• Choose Apple menu  > System Preferences, then click Keyboard. If ”Use F1, F2, etc. keys as standard function keys” is selected, target display mode uses Command-Fn-F2 instead of Command-F2. It might also help to use the keyboard that came with your iMac. Some third-party keyboards and older Apple keyboards don't support target display mode.
• Make sure that your iMac is using macOS High Sierra 10.13.6 or earlier. You can't use target display mode with later versions of macOS, or with Boot Camp and Windows.

Use your iMac as a display with target display mode - Apple Support

Note that there is one more requirement for using Target Disk Mode.

You have to be able to boot up the iMac normally to get to the point where you can put it into Target Display Mode.

So unless your Mac mini is running Catalina or earlier, and you can figure out how to get the iMac out of safe mode, there's no path forward for using the iMac as a display.

If this is a recent Mac mini, with a M1, M2 or M2 Pro chip, it won't be able to use the 2009 iMac either as a Target Display, or as a Target Disk.

Some 2009 iMacs support Target Display Mode using Mini DisplayPort input. But recent Macs, including Apple Silicon Macs, don't support using any iMac as a Target Display.

I believe that all 2009 iMacs support Target Disk Mode using USB or FireWire. None of them have Thunderbolt (they predate it) and so none can make Target Disk Mode connections using it. But a Mac running macOS 11 or later can only use another Mac as a Target Disk if the connection is a Thunderbolt one. There's no Target Disk Mode connection method that a 2009 iMac and an Apple Silicon Mac mini would have in common.

Why do you want to connect the Mac mini to the iMac...?

Is your goal to use the iMac as a monitor for your Mac mini? ... or something completely else?

Which exact model is your mini?