Using a 2011 iMac as a Monitor for a 2018 Mac Mini – Compatibility & Setup

1. No

If your MM has limited storage then add an External Hard Disk and move large libraries such as your movies, photos and music to the External Hard Disk. Apple explains the process in Move your Photos library to save space on your Mac.

To learn about AirDrop please refer to Use AirDrop to send items to nearby Apple devices - Apple Support

If the MM needs an addition external display, then simply buy one (they start at less than $100) and you are in business. This is MUCH wiser than attempting to use the 2011 iMac and less expensive as it does not require expensive cabling.

Yours is one of the very few situations where the use of target display mode on the iMac should work.

So, cautiously, I'll say yes you can use the iMac as a monitor for your 2018 Mac mini.

Only the following older iMac models could be used:

• iMac models introduced in 2011, 2012, 2013, and mid 2014 using Thunderbolt or Thunderbolt 2 cable.
• 24-inch and 27-inch iMac models introduced in 2009 and 2010 using Mini DisplayPort cable.

• The intended target iMac must be running macOS 10.13 High Sierra or earlier; it does not work with macOS 10.14 Mojave or later, or with Boot Camp and Windows.

• Retina display iMacs won’t work as target displays.

• In all cases the source Mac that you're connecting FROM must have been introduced in 2019 or earlier and have macOS 10.15 Catalina or earlier installed.

Here is Apple's guidance: Use your iMac as a display with target display mode - Apple Support

There is no capability to use another computer to resolve the performance issues of the iMac. Those problems will have to be taken care of on that machine. That could include installing macOS on an external drive and booting from that and possibly upgrading the RAM installed on the computer. There are other things that might help but those would best be addressed in a separate thread.

1. Yes. In your specific situation you can use the iMac as a display for the 2018 Mac Mini
2. You'll need a Thunderbolt 3 / USBC to Thunderbolt 2 adapter and Thunderbolt 2 cable.
   1. click here ➜ Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Amazon.com
   2. click here ➜ Thunderbolt 2(male) to Thundberold 2 (male) cable - Amazon.com
3. Not directly. If you do go for the Mac mini route, you will be entirely bypassing the iMac, and just using its screen as a display. The Mac mini is itself a complete computer and does not use the iMac's internals for anything. So basically the new Mac mini will be doing all the work, and yes it can do AirDrop and would have whatever storage you get it with and probably be a bit faster than the iMac. The iMac will continue to have the same performance issues. The Mac mini does not change or upgrade the iMac in any way.

See the following link to connect your iMac to a Mac mini for Target Display mode:

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

You probably can use your 2011 iMac as a Target Display for your 2018 Mac mini. However, you may find that doing so is not worthwhile.

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

• If this is a 21.5" or 27" Mid 2011 iMac, you will need to make a Thunderbolt connection, using, e.g., an $50 Apple Thunderbolt 3-to-2 adapter and a $30+ Thunderbolt 1/2 cable. An inexpensive USB-C to Mini DisplayPort cable will have plugs that fit, but will not provide the right kind of signal.
• If this is a 21.5" Late 2011 iMac, I don't know what the deal is with it. Both MacTracker and Apple's specifications (iMac (21.5-inch, Late 2011) - Technical Specifications - Apple Support) say that it just has Mini DisplayPort – not Thunderbolt. That says to me that the directions in the TDM article to use Thunderbolt can't be correct. Perhaps this "price point" model supports TDM using Mini DisplayPort input; perhaps it does not support TDM at all.
• A 2018 Mac mini running Mojave is just old enough to be a supported video source. If you had a Mac released in 2020 or later, it would not support using ANY iMac as a Target Display. If you were running Big Sur or later, those versions of macOS also would not support using ANY iMac as a Target Display.
• That old iMac would have either a 21.5" 1920x1080 display or a 27" 2560x1440 display. Given the prices of new displays, it might be better to take the $80+ you'd have to spend on specialized Thunderbolt hardware, and put that to use towards buying a real display.

Having just seen the post by user @rkaufmann87, I will add that their statements about storage, AirDrop and using a proper monitor for the Mac mini are correct. And I agree with their assessment.

While you can technically use that iMac and mini together, it really isn't the best use of the iMac. That is a computer and not especially well suited to perform as a monitor for another. A proper monitor will use less energy overall and will be much easier to setup and use with the mini. You also won't have to buy expen$ive cabling to use one.

Also, if you commit to using the iMac as a monitor, you also commit to limiting the true potential of the Mac mini. In order to use the iMac as display, your mini cannot run a newer macOS than 10.15 Catalina. In actuality, the mini is capable of running the newest macOS 15 Sequoia, an OS that is five years newer than Catalina and still receiving security and features updates and improvements.

I'll stand by my previous post confirming the technical ability of using the iMac as a monitor in your situation, but I do agree with @rkaufmann regarding the wisdom of not using that option and instead getting a proper monitor.

So, +1 to @rkaufmann's post. 👍🏽