2017 iMac 27 connecting to external displays

I have the same question. I just finished chatting with tech support and they said the 2 aren't compatible. I am wondering why the link (in the thread) doesn't indicate the lack of compatibility. Maybe someone has figured it out? I did send a complain to apple feedback.

Thanks for this very helpful reply. I bought the exact same monitor and cable based on this answer. Hooked it up to my 2017 5k iMac and it works like a champ after I adjusted the scale to get a better resolution. Totally happy that I found this and thank you for saving me so much time in researching a solution.

I believe Apple has some problems with TB3 and it's not admitting it.
There is NO single tb3/USBC to MDP/HDMI item one the market that is 100% working with Mac. I tried three myself. I would want to but a dock like OWC's or Bellini (this is sold on the official Apple store) but if you read reviews (on the apple store) they are totally negative. These products (that seem to work fine on PC) have inconsistent behaviour on Mac. I found a balance with a specific USBC device and now I know what to do to get it working 90% of the times (need to plug it in only once Mac is started). It's really a pity as a 100% working TB3 dock could be very useful

I have the same iMac and spent a weekend trying to connect to a DVI monitor. Trial and error... but I did find this one worked Amazon.com: USB C to DVI Cable (4K@30Hz), CHOETECH (6ft/1.8m) USB 3.1 Type C (Thunderbolt 3 Compatible) to DVI(24+1) Cab… (ASIN B06XCFPQH5) just plugged it in. Unfortunately they are out of stock right now...

I have just bought a 27-inch iMac, and to connect it to my 30-inch Apple Cinema Display I bought an AllSmartLife USB Type C Adapter, USB C Type to Mini DisplayPort/Mini DP from Amazon.com (Amazon.com: USB Type C Adapter, AllSmartLife USB C Type to Mini DisplayPort/Mini DP Adapter Cable With Aluminium Case Su…)

The adapter plugs into the USB-c port. You then plug in an Apple Dual-Link DVI to Mini-displayport adapter, and plug your screen into that. It works without problems

I have a similar cable the

USB-C to DisplayPort Adapter Cable 4K&60Hz 6ft/1.8m, ITANDA USB 3.1 Type C Male (Thunderbolt 3 Compatible) to DP Male 4K Cable for the 2016 MacBook Pro, 2017 MacBook, ChromeBook Pixel

But I cannot get it to work! I don't have the option on my imac Pro for a display arrangement! What did you do to get it to work?

Here's what FINALLY worked for me. ugh, it was so frustrating, I rad everyone's solutions and just couldn't make it happen. Multiple cables, adaptors zapping SMC nvram whatev's restarting etc, nothing But here's what worked -

I got this cable

CHOETECH USB-C to DisplayPort Adapter Cable 4Kx2K@60Hz (4ft/1.2m) for 2017 iMac, 2017

But it didn't work either UNTIL I did an SMC restart (shut down - unplug for 15 seconds - plug back in - wait 5 seconds - restart) WITH EVERYTHING UNPLUGGED IN THE BACK. After the restart (I had to plug my keyboard in to sign in) I plugged in the monitor and it worked.

Congrats! Must be nice. How do they compare when side by side? Your solution won't work with my 2, 11 year old Cinema displays!

I now have the 5k iMac 27 flanked by two ACD 23 inch up and running. Thank you again for your suggestions for the right adapter.

Has anyone with a 2550x1440 dual link DVI monitor been able to connect it to the new 27" iMac? If so, please share links to the adapter that went from 2017 iMac to dual link DVI.

Would this or something like this work to allow me to connect a iMac (Retina 5K, 27-inch, Late 2014) to my new 2017 5K iMac?

I want to use the older iMac as an additional monitor

That choetech also worked with external LG 27 UD68P-B and 2017-imac-27. Apple failed after a month.

Thank you! This worked for me.