Why You Probably Can't Use Your Old iMac As a Display
A common question is whether you can use your old iMac as a display for a new Mac mini, Mac Studio or maybe a second display for a MacBook. This is called Target Display Mode. Unfortunately, it only works with some older iMacs if you are connecting from older Macs and using specific systems. It probably isn't a good idea anyway as those older iMacs have screens that are not as good as what you can get cheaply today.