Hello, for years I am using my old 2010 High Sierra Imac in Tartget Display mode connected to a Mac mini. Works great. I have replaced my Mac mini with an IMac 2020 Catalina yesterday, use the same Mini Display cable (connected to Thunderbolt on new Imac) and it will NOT work? I want to use the 2010 IMac as a second screen just like it worked for my Mac Mini. The Thunderbolt port woks because it detects my external drive. Would could be the problem? Thanks for support.
Use your iMac as a display with target display mode - Apple Support
Officially, 2020 Macs can no longer take advantage of a iMac as an external monitor. However, a recent post suggests it may still work with a 2009 or 2010 iMac. See this thread:
https://discussions.apple.com/thread/251704486
However, most responders say that they cannot make it work. If there is a problem with your setup outside of the 2020 issue, I'd say it was the Mini-display cable. Try a Thunderbolt 3 cable with any adapters at the old iMac's end.
⚠️ Note that you can pay a lot of money for the T3 cable and still not have this work. Caveat emptor!
Use your iMac as a display with target display mode - Apple Support
Officially, 2020 Macs can no longer take advantage of a iMac as an external monitor. However, a recent post suggests it may still work with a 2009 or 2010 iMac. See this thread:
https://discussions.apple.com/thread/251704486
However, most responders say that they cannot make it work. If there is a problem with your setup outside of the 2020 issue, I'd say it was the Mini-display cable. Try a Thunderbolt 3 cable with any adapters at the old iMac's end.
⚠️ Note that you can pay a lot of money for the T3 cable and still not have this work. Caveat emptor!
Target Display mode
