Does Big Sur break Target Display mode from 2015 5KiMac to a 2009 iMac?

[arbitrage]

I have been reading up on people not being able to use TDM anymore on Big Sur with M1 macs. There was discussion that Big Sur eliminated TDM for good. But then other reports seemed to say that the iMacs without TB ports could still be used (like my 27" 2009 iMac).

I currently run my 2009 27" iMac (on El Capitan) in TDM from my late-2015 5KiMac (on Catalina). I want to upgrade to Big Sur on the 5KiMac but don't want to break TDM to my 2009.

Can anyone confirm that it still works this way.

 

[chabig]

It should work. In your case, only the 2009 iMac needs to support target display mode. The 2015 iMac simply sees the other machine as a display.

 

[joevt]

I have been reading up on people not being able to use TDM anymore on Big Sur with M1 macs. There was discussion that Big Sur eliminated TDM for good. But then other reports seemed to say that the iMacs without TB ports could still be used (like my 27" 2009 iMac).

Since the 2009 iMac uses DisplayPort for TDM, it appears as a normal DisplayPort display, and any computer/OS should be able to use it, Mac or PC.

For newer iMacs (2011-2014) that support Thunderbolt TDM instead of DisplayPort TDM, only a Mac with Thunderbolt port running macOS can use the iMac as a display.