Connecting iMac to Mac mini

it's not possible, the imac can have external monitors connected but it can't act as a monitor for other device

at least not as primary monitor

the third party way to have it act as secondary monitor for the mac mini perform poorly people repports

Use iMac as monitor: 5 Solutions - 9to5Mac

and an imac acting in this manner will still use as much electricity as when it just being a computer, so rather wasteful compared to a normal monitor

+1 No, a new Mac mini can not use your 2017 iMac for the setup or primary display.

If you buy a new Mac mini, you will need an External Display or Hi Resolution HDMI TV.

see > Connect displays to your Mac mini - Apple Support

Target Display Mode went away in Late 2014 when the first 27" 5K Retina iMac came out. Your 2017 iMac doesn't have it. Apple also added restrictions such that no current or recent Mac supports using any iMac – even an older one – as a Target Display.

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

Your iMac is also too old to support being an AirPlay Receiver for AirPlay to Mac, a lower-quality method of using a Mac's screen.

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

Others have assumed you were asking if you could use your iMac as a display for a Mac mini. The answer is NO.

However, if you are asking if you can connect the two Macs to 1) migrate from the iMac to the new mini, 2) share or transfer data, or 3) do Screen Sharing, the answer is YES.

• Transfer to a new Mac with Migration Assistant - Apple Support
• Set up file sharing on Mac – Apple Support (AU)
• Share the screen of another Mac – Apple Support (MY)

Note that Screen Sharing is not a substitute for a directly-connected monitor. You do need a directly connected monitor attached to a Mac mini.

"Connecting iMac to Mac mini: TOPIC CONNECTING IMAC TO MAC MINI: I have a 2017 iMac Processor 3,4 GHz Quad-Core Intel Core i5 Memory 8 GB 2400 MHz DDR4, Serial Number***. HD 1.03TB, Can I connect the iMac to a new Mac mini I am consdering buying Thanks Roger"

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Transferring Data by Connectivity:

Hardwired:

If you could power these on, then a crossover cable may work (USB-A to USB-A) or Ethernet. If that does not permit this, then see if it is at leased seen by both Macs.

1. Hold Down: option key
2. Click: Apple menu
3. Select: System Information
4. Select: Ethernet
5. Look: for this coinciding Mac
6. Select: USB
7. Look: for this coinciding Mac