TDM configuration

Use your iMac as a display with Target Display Mode - Apple Support - https://support.apple.com/HT204592 - iMacs late 2009-Mid 2014

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/252311206?answerId=254372593022#254372593022

and read about Screen sharing https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/mac

Limnos wrote:

and this 2021 post by Allan Jones about software limitations:

https://discussions.apple.com/thread/252311206?answerId=254372593022#254372593022

Thank you, Limnos.

That response was specifically for the OP in the other thread who had an older MBP. I've created an overview version that I hope is less obfuscated than the archived Apple support article.

VIDEO SOURCE COMPUTER (the one sending the video signal to an external monitor):

• • A 2019 or older Intel Mac running macOS 10.15 Catalina or older.
  • Apple Silicon Macs are not supported
  • mac OS11 Big Sur is not supported.

TARGET COMPUTER (the one to be an external monitor):

• • An iMac 27-inch (Late 2009 and Mid 2010)
  • any iMac from Mid 2011 to Mid 2014.
  • The target computer must run no higher macOS than OS 10.13.X High Sierra.

⚠️ NOTE: Since I put that together, I have seen one post here where a user claims to have TDM working under Big Sur from an Intel Mac to a supported iMAc, but all other user info here and that from one of our Hosts says it does not.

A 2020 MM will not support TDM. If your MM needs an external display please buy one.

I'll update my reference to this post, thanks.