I have a 24" 2021 M1 iMac and a 21.5" Late 2013 Intel iMac. I'm trying to use the former as main computer and the latter as an additional screen.
I bought a Thunderbolt 3 to Thunderbolt 2 cable, and a Thunderbolt Cable. Connected both and my 24" didn't detect the 21.5".
How do I properly set this up?
iMac 24″, macOS 13.1
Welcome!
Unfortunately, you cannot Use your iMac as a display with target display mode - Apple Support:
iMac models introduced in 2011, 2012, 2013, and mid 2014
To use any of these iMac models as an external display:
The iMac used as a display must have macOS High Sierra or earlier installed.
The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
The cable connecting the two Mac computers must be a Thunderboltor Thunderbolt 2
Your new iMac was introduced in 2021, and will be running macOS Big Sur or later.
However, Luna Display, a third-party solution, might work well for you: Luna Display | Turn your Mac or iPad into a second display.
Jack
Welcome!
Unfortunately, you cannot Use your iMac as a display with target display mode - Apple Support:
iMac models introduced in 2011, 2012, 2013, and mid 2014
To use any of these iMac models as an external display:
The iMac used as a display must have macOS High Sierra or earlier installed.
The other Mac that you're connecting it to must have been introduced in 2019 or earlier and have macOS Catalina or earlier installed.
The cable connecting the two Mac computers must be a Thunderbolt
Your new iMac was introduced in 2021, and will be running macOS Big Sur or later.
However, Luna Display, a third-party solution, might work well for you: Luna Display | Turn your Mac or iPad into a second display.
Jack
Adding 21.5" Mac as additional screen to 24" Mac
