Retiring a 2019 iMac to be used as display only

cotterfahey wrote:

I am thinking about getting a Mac Studio and use this old iMac as the display. The question is, could this iMac run as a display without the dreaded fan noise? Is there a way to shut down the processor once it is plugged in?

No. It cannot be used as a display for the Mac Studio directly and even if it could, it would need to be on, and the fan would come on if the CPU is getting hot and needs to be cooled down.

Forcing the fan to turn off will just end up with a toasted CPU, and a broken iMac.

Sell the iMac, and buy an actual display instead.

Target Display Mode went away when the first 27" 5K Retina iMac came out in Late 2014. Your iMac does not have it, and no current or recent Macs have support for using ANY iMac as a Target Display.

That 2019 iMac is new enough to be an AirPlay Receiver for AirPlay to Mac, a lower-quality method of using a Mac as a display. However,

• This will not get rid of the need for at least one real monitor – since if you do not have a real monitor, you'll have no way of telling the Mac Studio to AirPlay to the 2019 iMac.
• AirPlay will not take full advantage of your 27" 5K screen and you may find the quality to be unacceptable.
• There is no way to shut off the processor that will not also shut off the iMac's ability to act as an AirPlay display.

Continuity features and requirements for Apple devices - Apple Support

There is a third-party workaround product called Luna Display that might let you use that 27" iMac as a second display. But there, too, you would need at least one real monitor; there would be compromises; and you would not be able to shut off the processor (and any associated "dreaded fan noise").

No.

The iMac cannot be use as a monitor for any new Mac, nor PC.

This is no longer supported by Apple in the macOS nor in hardware.

Apple killed target display mode hardware when the first Retina Macs were released in 2014 and the feature died in software with the release of macOS 11 Big Sur.

Using an iMac As A Monitor (Thank you, John Galt)

cotterfahey wrote:

The question is, could this iMac run as a display without the dreaded fan noise? Is there a way to shut down the processor once it is plugged in?

No. You can't use it as a display at all.

the good news is that a real monitor uses a fraction of the power that an imac acting as display port screen would, so it's the environmental path really