Tested, iMac 2020 STILL supports target display mode with older iMacs, advice for other people:

Hi,

I have the same combination but it is not working. I was previously using a 2018 27" iMac to the same second monitor.

What ca

Cable are you using?

.

I got Imac 2020 and 2012. I confirm the targeted display mode does not work. Anyone know how to fix this? otherwise, I have to sell my Mac2020.

I’d like to hear about Luna also, as my newer Mac is likewise sitting on a desk as decoration right now.

Luke, please keep us informed on what you hear. I already have Duet Display purchased and I'm going to try to make that work on both iMacs.

Any update? Have you gotten it to work?

What is the issue? I mean why cut the support of it when older mac an be such an asset?

Thanks for the report! :) 👍

OK, the file I was trying to upload was an HEIC file. I have exported the picture as a simple .jpg and will try to post that in a follow on post.

Hi Zahilla

Have you upgraded to Big Sur and does it work? Thanks!

I already had target display mode working to 27in iMac mid 2011 from a 27in 2018 iMac (10.13.6) using a thunderbolt3-thunderbolt 2 connector. Switching to the new 2020 iMac with the same cable and same 2011 old iMac it no longer works.

iMac 2020 cannot be set as a Target Display from another Mac machine. I think that is the problem. I have been trying to use my 2020 iMac as an external monitor for my 2019 MBP. It does not work. I spoked to an Apple Sr. Advisor and he told me it would not work either.

Hi Zahilla,

I am trying to use 2020 retina iMac as source and 2012 iMac as TDM monitor but it does not working yet. Interestingly it works when I use a MacBook as source so I guess there is a problem in source iMac or in cables.

Can you provide more details of the cable? I am trying it with Thunderbolt 3-to-2 adapter and a Thunderbolt 2 cable.

That's exactly what I was trying to do only my second iMac display was a 2017 iMac. Tried every known cable and MacOS configuration. Never worked. Apple confirmed that the 2020's won't work in TDM. Finally hooked up an older 2010 iMac to the 2017 in order to get two displays. Now the 2020 sits lonely on the other desk. Will sell back at some point.

Paul, although the posts above contain some back and forth on the issue, the final consensus appears to be that 2020 iMacs do not support Target Display Mode. Apple has offered up their own software to allow iMacs to use iBooks or iPads as a second screen (built-in functionality is called Sidecar), but Sidecar is not supported on iMacs until after 2015. So, in terms of an Apple solution, I think we're SOL. It would appear that the Luna Display dongle and software may offer a workaround to this. For $80 of hardware this would appear to offer Mac to Mac screen sharing for a source computer running Catalina and the TDM computer running any IOS after Mountain Lion. I am trying to get some feedback from other users who may have attempted this fix. But I already have $100 invested in cables and days of my time, so I'm in for another $80 if it works.