2015 27-inch iMac as display for M5 Mac mini

Don't be confused any longer. Hundreds of users have posted similar questions over the last few years, and several today even, about using current Mac Minis with older iMacs in target display mode and it is physically not possible because Apple's Target Display Mode support ended after the 2013 iMac. And the iMac is a computer, not a display.

Now, you purchase a proper display at the resolution and size that fits your budget and connect that to the Mac Mini with an Ultra-speed HDMI 2.1 4K cable. That is what I did with the M4 Mac Mini Pro (there is no M5 mini yet) using a 32-in LG 4k Display. I recycled my 2013 27-in iMac at the Apple Store.

Confused_42 wrote:

Can I use my 2015 27" iMac computer as a monitor connected to a new M5 mini Mac?

Not using Target Display Mode. That feature went away in Late 2014 when the first 27" 5K Retina iMac came out. There simply is no port on the 2015 iMac that is designed to let an external device use that iMac as a monitor.

See the bad news here: Use your iMac as a display with target display mode - Apple Support

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Not using AirPlay to Mac (a lower-quality way to use a Mac as a display). That iMac is too old to support being an AirPlay Receiver.

See the bad news here: Continuity features and requirements for Apple devices - Apple Support

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There is a third-party workaround product called Luna Display that might let you reuse that old iMac as a second display. You will still need at least one real monitor. The connection is not as good as with a real monitor and the vendor themselves acknowledges that the product has limitations.

"Like any product, Luna Display does have limitations and it’s not recommended for high-motion content. For example, I wouldn’t recommend using Luna Display for gaming or video editing.

Since Luna Display is squeezing a 5K display through a USB cable, when lots of motion occurs on-screen (like from video playback or moving a window quickly) the screen can temporarily become pixelated before it renders in at full resolution."

Astropad – Blog – How to Use Your iMac as a Monitor: A Step-by-Step Guide [2025]

My advice would be to choose a monitor (or pair of monitors) for your M5 Mac mini which you would be happy to live with as your only monitor (or pair of monitors). Then, if you wanted to try to add your 2015 iMac as a second monitor or third monitor using Luna Display, you'd have a good setup to fall back to if that did not work out.

Nope! If you have or purchase a new Mac mini..? Then you will also need an external display that supports HDMI, USB-C or DisplayPort input. see > Connect a display to Mac mini - Apple Support

no, well not as it's primary monitor

there are ways to use it as a secondary monitor

https://9to5mac.com/2024/02/02/use-imac-as-monitor/

but it will use a lot! more power than a normal monitor as the whole computer would

be running.