I have a new iMac (27-inch, Retina 5k display 2020, Big Sur 11.2) to which I'm trying to connect an old iMac (27-inch, late 2013, El Capitan 10.11.6) as a second monitor. I'm using a USB-C adapter and Thunderbolt 2 cable to connect the two iMacs. I've followed every online tutorial to troubleshoot this, including testing the adapter and cable. Why is it not working? Could the USB-C port on the new iMac be bad?
iMac 27″, OS X 10.11
Read this:
Use your iMac as a display with Target Display Mode - Apple Support - https://support.apple.com/HT204592 - iMacs late 2009-Mid 2014. HOWEVER, this document is "archived" which means this feature is no longer supported on the new line of Macs and operating system versions that are currently supported by Apple. The document is basically there if you have all equipment and system versions to be used dating from that era.
This could only be done with a very few and very specific older iMacs and support was very limited. Read this topic for a 2021 perspective on this: https://discussions.apple.com/thread/252271436?answerId=254300142022#254300142022
and this 2021 post by Allan Jones about software limitations:
https://discussions.apple.com/thread/252344497?answerId=254428494022#254428494022
and read about Screen sharing https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/mac
Read this:
Use your iMac as a display with Target Display Mode - Apple Support - https://support.apple.com/HT204592 - iMacs late 2009-Mid 2014. HOWEVER, this document is "archived" which means this feature is no longer supported on the new line of Macs and operating system versions that are currently supported by Apple. The document is basically there if you have all equipment and system versions to be used dating from that era.
This could only be done with a very few and very specific older iMacs and support was very limited. Read this topic for a 2021 perspective on this: https://discussions.apple.com/thread/252271436?answerId=254300142022#254300142022
and this 2021 post by Allan Jones about software limitations:
https://discussions.apple.com/thread/252344497?answerId=254428494022#254428494022
and read about Screen sharing https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/mac
Per the previously-linked Target Display Mode document:
“You can connect any of these older iMac models to another Mac from 2019 or earlier for use as an external display.”
The article wording is atrocious, but your 2020 display-source iMac is too new.
Second Monitor connection
