There is literally nothing stopping you from using a modern iMac as an external display using a thunderbolt connection today.

If you're OK with video compression artifacts, you can even do it over a WiFi connection.

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Forgeties79 an hour ago | parent [-]

You cannot grab an iMac, plug it into a silicon Mac, and get a picture on the iMac (without 3rd party software). This is incorrect. Please go look this up. The feature stopped working when silicon Mac’s came out. It only works on Intel Macs. 5K iMac or not.

Target display mode, the feature that allowed this, is no longer supported.

	▲	GeekyBear 35 minutes ago \| parent [-]
		> without 3rd party software At least you can finally acknowledge reality. Also, VLC over a wired connection and streaming from one Mac to another using WiFi (AirPlay) are built into the OS.