Target Display Mode not working 2020 MacBook Pro (Catalina)

All iMac models introduced in 2011, 2012, 2013, and mid 2014: Use a Thunderbolt cable to connect your iMac to a Thunderbolt or Thunderbolt 2 port on the other Mac. If the other Mac uses Thunderbolt 3, you can use the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with your [genuine ThunderBolt] cable.

from:

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

That's a genuine ThunderBolt cable, right, not just a Mini DisplayPort cable?

No. The newest iMac supported is an "old" 2014 model.

iMac models from 2015 or later will not work, EVER

and 2020 MacBook Pro and newer models will not work, EVER

You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display. Learn how to identify your iMac model.

• • • 27-inch iMac models introduced in 2009 and 2010: Use a Mini DisplayPort cable to connect your iMac to a Mini DisplayPort or Thunderbolt or Thunderbolt 2 port on the other Mac.
    • All iMac models introduced in 2011, 2012, 2013, and mid 2014: Use a Thunderbolt cable to connect your iMac to a Thunderbolt or Thunderbolt 2 port on the other Mac. If the other Mac uses Thunderbolt 3, you can use the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with your cable.

Target display mode requires macOS High Sierra or earlier on the iMac used as the external display. It does not work with macOS Mojave or later.

from:

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

According to what Apple Support told me today after some tests with them (and chasing them for a couple of weeks), Target Display Mode does NOT work with MBP 2020 13'' + iMac 27'' late 2013. They kind of apologized for the misleading information on their website (I really looked this up before purchasing the MBP), so I don't think that there will be any fix in the future.

Will Target Display Mode feature be re-enabled? Obviously the user community is furious, and so am I – our brand new 2020 MacBook Pros are useless at the office with an existing iMac as a perfectly usable display. Can anyone more tech savvy from the Apple support chime in on the issue, please?

—Target display mode not working, I want to set up an old iMac (mid-2011 running High Sierra) as an external monitor for my new 2020 MacBook Pro (running Catalina)...I am using a brand new 2020 MacBook Pro, USB-C to Thunderbolt adapter, Thunderbolt cable, plugged into the iMac's Thunderbolt port (not mini display).

The support article on TDM that Grant links says this:

—I am quite unhappy that this appears to be apple purposefully rendering old products obsolete by not including backward compatibility software/code.

Tell Apple: Feedback - macOS - Apple

—Will apple fix this in a software update?

We are not Apple but end users like you. Based on the fact that Apple started the deprecation of Target Display Model in Late 2014 and completed it early this year, I would say "chances are slim."

I think all the confusion over TDM was a lack of journalistic research, and not a plot by Apple. Prior to COVID we saw 1-2 posts a MONTH about TDM. Now we see a dozen or more a DAY. I believe some overzealous journalist saw a quarantine opportunity and posted about TDM as an option for people working and from home, but forget to look up the sysreqs and history that would show TDM is a dead issue.

After spending hours troubleshooting with Apple Support to address this exact same issue, it turns out the feature is only supported for 2019 MacBooks and older. In this article https://support.apple.com/en-us/HT204592, last updated in April 2020, they exclude the 2020 models: "You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display." No proper reason given, only "We apologize for the inconvenience", and "This is how the market works" responses.

This is the Apple User-to-User Support Community. Apple, Inc makes no promise to read these threads, and never responds here except to be sure your posting was not completely ignored. There is no guarantee of follow-up in this forum.

If you want to communicate with Apple, Inc, you can use the feedback link to post your [terse] thoughts:

Product Feedback - Apple

if you want a response from Apple, Inc, you need to use the "Contact support" link at the top of every forum page or call their toll free number.

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If you like, you Can use screen sharing to share the screen of any Mac on your local network in a window on another Mac.

https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/10.15/mac/10.15

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You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display. Learn how to identify your iMac model.

from:

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

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I have a mid-2014 iMac and a 2020 Macbook air. Apple told me to purchase a Thunderbolt or Thunderbolt 2 port for the iMac and a Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter to connect the two displays. The displays do not work and they still can't seem to help me, so I need to return the cable and adapter. No idea how else to connect them.

Just a theory here - but maybe if you have a USB HDMI capture device you can run a a cable from your MBP to your iMac. So the signal would go:

• MBP USB-C output to:
• USB-C to HDMI adapter to:
• HDMI cable to:
• HDMI capture device plugged in to:
• iMac

Then you'd run the capture stream full screen

Dear Grant,

Since you seem well aware, and at least a lot more than the apple support online people in France (who with I spent ages on call and noone told me before I found this thread). Then maybe you will know the answer to my next problem then:

Since my iMac cannot be used as TDM, forget it... I then yesterday bought an Apple 27" Thunderbolt 2 LCD display (second hand).

And it does the same: it works fine on an MPB 2012, 2016, but not on my brand new MBP 2020.

Apple support online spent 1h44 min with me yesterday. And they offered to call me back today. If it's not compatible this time it's not written anywhere. And so they confirmed.

If I also look in my MBP2020 in apple/About/Support/SPecs.... video support, then after all the trendy 6k and 5k, it also reads:

• "VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)"

So this is supposed to work fine isn't it? Of course I repeat the screen works fine on older MBP and not on the most recent one. I use only apple adapters.

So this one is good for the bin as well then? Why is it not written anywhere?

Or is it again that there was not enough room in the ROM in a laptop that costs $4k...

let's clear somethings up once and for all:

TargetDisplayMode to any Mac works with (from) any Mac or PC as host device, so long as it's not Thunderbolt on the first mac.

Any Mac with Thunderbolt 1/2/3 AND TargetDisplayMode will only work with Macs and Pc’s of similar standing, so TB1 to TB1, TB2 to TB2 etc, because of the way that Thunderbolt works, backwards compatibility or forwards compatibility, display-wise is not something you should rely on when buying a new Mac hoping to use an old Mac as display.

I won't go into to much detail as to why it won't work, but suffice it to say it's because of the way Thunderbolt works and in the manner it's able to carry certain protocols to and from computer to displays such as HDMI, DVI, DisplayPort etc. and because of this interplay and such things as HDCP requirements it may and may not work with the plethora of diverging setups ya’ll got out there.

Now, onto what DOES work in regards of Target Display Mode:

All Macs of any year that are able to connect over Thunderbolt, HDMI, DisplayPort (likely mDP) or DVI (likely mini-DVI) are able to send video out to any older iMac or MacBook without Thunderbolt BUT with a HDMI, DVI or DP connector.

So the following scenario/example, from my setup goes:

A 2020 MacBook Air/Pro M1 or 2020 Mac Mini M1 to an 24-inch iMac 2008 using Mini DVI and iMac 27 inch 2010 with Mini DisplayPort.

In both of these cases, such an older iMac, when booted up and logged in to macOS, can be set to TDM using cmd+F2 on the keyboard (of the Mac you are going to use as a monitor), at that time, such a Mac will present itself as a vanilla DVI or DP monitor to any host computer, in my case those M1 Macs. All you need to do is provide the proper cable and adapters to connect them, in my case a DisplayPort to Mini DisplayPort cable (with bi-directional support) that goes into a caldigit TS3 Plus dock, which has a standard DisplayPort connector on it.

At that point, the TB3 that comes out of the Mac is first passing through the dock, and then it will provide the DisplayPort signal. of course direct connection is also possible, you just have to find the right cable for it, most likely a apple or belkin type branded tb3 usb c to either hdmi, DisplayPort, dvi, etc cable whichever you need to connect that TDM mac's port to it. But it does work.

Again, so long as the Mac you want to use as a display didn't have any version of thunderbolt shipped with it, because then, as explained above, you're gonna run into connection issues as Thunderbolt will be the limiting factor in interoperability.

I hope this helps for others. AS far as my setup is concerned, the iMac screens I'm using are both fully recognised, with the right color profile etc, and on the 27 inch iMac with the mini Display port connector, it even sends the audio along to that mac's built in speakers if I want to:

Color LCD* is how my 2010 27 inch iMac appears in the audio prefs pane

...and as just 'iMac' under my display prefs panel.

(*Which I rarely use, most of the times, I use the SPDIF to send the audio to Sonos for surround experience or in this case just using headphones)

Also currently the 2008 24 inch won't turn on anymore, but before that it was connected tot my M1 Mac mini using an apple adapter which gives a mini dvi connector, this setup won't carry audio though, as it was not part of apple's mini dvi implementation on those Macs at the time)

ah it's been a while since I've posted here, I can say to start with: the cable in this case really matters, try a thunderbolt 3 to (mini) displayport cable and make sure the cable is marketed as bi-directional, most of the times, the cable is not bi-directional and this would prevent a connection and the necessary HDCP-handshakes.

As TDM in combination with Thunderbolt 3 or newer Macs has been a hot issue on here and elsewhere, which Apple still has failed to address, I can at least provide the following update from my perspective and setup, after which I'll reply to karinavans' specific issues.

But, suffice it to say if you have an {i}Mac with Thunderbolt you want to use as a target display for another Thunderbolt mac, you can't {in most cases} because of limitations of the DisplayPort and HDMI protocols when run over Thunderbolt. Only a small subset of such macs that shipped with first and second gen Thunderbolt might work OOBE with similar class macs.

Now IF, and I stress IF, you like me are lucky to still own a pre-Thunderbolt-era Mac with built-in display that either uses Mini DVI or mini DisplayPort as is the case with my 2010 27'' iMac, then yes, you can indeed use the screen as a display for other macs, even other non-Apple computers (really**), as it would present itself just as a vanilla generic DVI or DisplayPort monitor with digital audio path (in the case of mDP Macs) to any computer upon activating TDM from the active, running copy of MacOS on that mac.

So a fully working mac (with built-in display) with a valid install of whatever version of macOS it happend to ship with or later version it still support, is indeed needed, also in most cases, you won't have to login on the mac you want to use as a display, just make sure the mac is fully booted up and on the login screen, when you want to active TDM with the official keyboard command.

So keep that mac around if you ever switch to a macbook :_)

Now to re-cap to karinavans' issue, as I've stated above, the cable really matters, because most of the failures come from the cable not being manufactured up to snuff. And yes, the cable has to be marketed as bi-directional.

For my specific setup the dock is the Caldigit TS3 Plus, which has it's own Thunderbolt chipset and comes with a native DisplayPort connection, that is connecting the iMac to the MacBook, the cable used is the Rankie Mini DisplayPort (Mini DP) to DP-Cable as sold on Amazon. this setup works as you can see in this photo:

(the monitor on the right is not in use with the Macbook, but rather connected to an ISP's tv settopbox via hdmi, photo is recent, dated 23rd of May)

I hope this clarifies things for everyone here.

You can spot a bit of the TS3 on the left, behind the macbook's display.

Television feed on the iMac monitor is coming from a USB DVB-C tuner stick connected to the caldigit dock icw Eyetv software.

I have a 2010 27" iMac and it is working fine in target display mode with my new 2020 MacBook Pro 13". My 2013 27" iMac does not work in target display mode with my new 2020 MacBook Pro 13".

So, it seems to support display port, but not thunderbolt.

Both iMacs worked fine in target display mode as a dual setup with my 2017 MacBook Pro 13", but not the 2020.