Target Display Mode not working 2020 MacBook Pro (Catalina)

well, you are party right, display link does create a so called virtual graphics card in memory on cpu/gpu and uses compression to send out video over usb, then de-compresses it inside the used dongle, box or dock which is a display link certified-chipped product yes, which it will indeed decode that to the video signal a display needs, i.e. displayport, vga, hdmi, dvi etc.

But displaylink has come a long way in recent years, is widely supported on Mac, pc & linux, already sporting resolutions of up to 4k@60hz in multi monitor configurations and up to 5Kp60@30Hz in single monitor setups, depending on accessory type and make. Also dropped frames with the latest kits from the more common, top brands such as wavelink, plugable, startech & cable matters is mostly a thing of the past, due to in large part because of the enormous additional bandwidth that USB 3.1/3.2 and Thunderbolt 3 afford. (Completely ignoring the move to USB4 at this point, kicking off just about now, which is gonna make it better yet still to come...)

Also, as seen in the various youtube videos and multiple benchmarks, especially on the new M1 macs, it runs just as good as dedicated ie. native monitors would, due to the way the M1 handles encode-tasks with it’s high‑performance and high‑efficiency cores, while DisplayLink’s bandwidth adaptive codec is indeed proprietary to them and their partners, it’s also very similar to how the M1 does H.264 or H.265/HEVC encodes, which of course it does natively. 

So really, if you’re not doing anything crazy, like those hub/dock buyers you describe, who I asume moste likely cheaped out on the first dock they could find or are doing things like trying to add all the 4K HDR displays they can, you should be fine for most use cases nowadays anyway. If you limited the amount of moniters you use with display link of course.

See it like this, instead of watching to a native uncompressed video output, you're seeing your computer like you do Apple TV+: compressed video, which again, is fine for most people and use cases.

You make some good points.

Apple so far has stuck to their: 'no delays, no dropouts, cinema quality' standard on the Mac. As displays get bigger and bigger, and the hardware requirements (especially memory speeds) become more torturous, whether enforcing Apple's standard as THE single standard available is the correct choice for everyone is certainly debatable.

Using DisplayLink displays for your secondary displays allows you to think differently. But in suggesting these alternatives, we must NOT gloss over the fact that the quality may be somewhat different than the standard Apple espouses. Deciding to use DisplayLink displays should be an Educated choice.

yeah, I myself plan to use it to add only one 1080p1200 dell display to a macbook, while using the native connection to connect a regular displayport 27'' display using apple thunderbolt to displayport cable to the same macbook natively. so i think i'm good, even when watching netflix and such on the 1080 dell screen

i do of course agree, it has to be an informed choice here.

I have same issue Target display mode not working with set up an old iMac (mid-2011 running High Sierra) as an external monitor for my new 2020 MacBook Pro (big Sur).

I connect 2020 MacBook Pro with apple thunderbolt display with same cabling for IMAC 2011 and work fine

issue with 2020 MacBook Pro to iMac (mid-2011)

I found this option that can be used to connect old Macs to new Mac over WiFi - Astropad Luna Display

It professes to work in Mac to Mac mode with display source Mac from 2011 or later, and display target Mac from 2007 or later. It support Macs with Apple M1. It also allows iPad to Mac mode which looks nice especially for using an Apple Pencil for drawing.

It is over WiFi so I imagine it isn't great for gaming, and maybe not for video editing - however they claim 16ms latency.

At $80 it is a bit more expensive than cables, but much cheaper than additional monitors - and its also pretty tidy to go wireless.

I haven't tried it myself (they don't currently ship to the UK because our import processes are a mess right now) but thought others here might find it useful.

You don't need ANY extra equipment to connect two Macs (through your Router) over Wi-Fi -- just enable File sharing in Sharing preferences.

The drawback is that for large volumes of data, it can be very slow... like DAYS.

Hello,

I've re-read your post a couple of times to ensure I understand everything -

However, I'm not sure if I'm confused or if this is incorrect. But I want to make sure I've exhausted all my options with this issue before I go ahead and invest more money by purchasing the "astroluna pad" I've been seeing recommended on this thread.

Attempting to connect:

Early 2009 iMac as display <-> with <-> 2020 Macbook Air

I can confirm:

My Early-2009 iMac does not use a thunderbolt.

Using cmd+F2 on iMac does nothing when direct connecting with a:

USB C to Mini Displayport Cable.

Also, you mentioned a "dock". Possibly adding this (vs a direct connection) might help but I'm unsure as to what kind of dock you are using with your set-up?

Any help would be greatly appreciated! Thank you!

I'm in the same boat. I relied daily on this with my 2017 MBP, and it seems reasonable to expect that it would continue to work with the new MBP 2020. It would be good to know at least why it's been disabled, and whether there's any plan to reenable, so that those of us in this limbo can make an informed decision about how to remediate. It also seems reasonable to expect Apple to be aware of the scale of impact this would have. With all of the diagnostic data that many of us share with Apple, not to mention the popularity of the "How to use iMac as target display from MBP" topic on various forums, it's disappointing they didn't take better measures to protect users.

I'm having the same issue. I have a machine that is outdated but still good as a monitor and it's destined for landfill for NO REASON whatsoever. Shall we take this to the media perhaps? Apple is supposed to be a leader with regards to environmental practices. Very disappointed indeed.

How did you do this? I have a 2010 iMac that I want to use as a TD, and a 2020 MacBook Air. I plunked down the $100 for the Thunderbolt cable and Thunderbolt 3 to Thunderbolt 2 adapter, and it still doesn't work. Running OS 10.7.5 on the iMac and OS Catalina on the MacBook Air.

I ultimately went for Luna Display app... works like charm! https://shop.astropad.com/ Makes my 2009 iMAC a display for my13" Macbook Pro. Easypeasy! I gather that is why Apple won't bother to support it as there are others doing it better I guess? I tried unsuccessfully for over a year... had to move on.

Both are Apple issued, the cable and adapter. It works fine from the 2017 MacBook Pro 13, just not the new 2020 model.

Apple makes no promise to read the items posted on these User-to-User support forums. But they DO read items posted here:

Product Feedback - Apple

Don't be too wordy, there's a limit.

the following screenshot shows my setup's technical details:

(compression artifacts due to apple's forum software, hi res available upon request if needed)

Did the customer support tell anything on if this would work with a newer iMac? I have a new MacBook Pro 2020 but an 2012 iMac and am facing the same problem.