In the latest TestFlight build v7.3.203 from the Channels for Apple TV 4.0 Beta, we have added a new setting:
Settings > Playback > Advanced > Video Driver: Experimental
With this enabled (and
Match Content > Match Range: Yes set on your Apple TV settings), imported movies in 4K UHD HDR10 will switch the TV into HDR mode and will play back with full HDR colors.
Share your experiences with the experimental video driver below.