Target display mode appears to require a <4K ThunderBolt or DisplayPort connection. Apple TVs exclusively use HDMI output, but Apple sells ThunderBolt to HDMI adapters. I was wondering if it would possible to use one of those to display Apple TV content on an iMac. However, these adapters always seem intended for use with ThunderBolt input and HDMI output.
I don't know if it's possible to use any adapters to produce ThunderBolt output. Even if it is, I'm not clear whether the iMac can be used with arbitrary ThunderBolt video input, or whether it requires some additional metadata or protocol that must come directly from another Mac.
Is there any iMac which may be used in target display mode be used as the display for any Apple TV, with the right configuration and adapters?