Apple brought expanded AirPlay to Mac computers with macOS Monterey, and it reportedly can be used to turn Mac computers into second displays.
According to MacRumors, the updates to AirPlay allow Macs running Monterey to AirPlay content to other Apple devices, including iPhones, iPads and, most importantly, other Macs. MacRumors says it confirmed that users can extend or mirror their Mac display to another Mac using AirPlay, effectively allowing any Mac computer to function as a second external display for any other Mac.
Further, the macOS Monterey features page notes that AirPlay to Mac works both wirelessly and over a wired connection using a USB-C cable. Wirelessly should work fine for most people, but using a cable could help cut down on any latency.
This is as close as Apple has come to resurrecting the old ‘Target Display Mode‘ feature, which allowed some 2009 to 2014 iMacs to serve as an external display for another Mac. That said, Mac-to-Mac AirPlay isn’t a perfect solution — AirPlay does compress video sent from one Mac to another and likely has some latency issues, especially over a wireless connection.
Still, it’s a great add and could come in handy for many people who have, say, an iMac desktop and a MacBook. It’d be an easy way to quickly upgrade your workstation into a multi-monitor setup. Of course, if you don’t already own two supported Mac devices, it would likely be cheaper to just buy a second monitor instead of a whole new Mac.
Mac-to-Mac AirPlay requires a 2018 or later MacBook Pro or Air, a 2019 or later iMac or Mac Pro, an iMac Pro or the 2020 Mac mini.