A:Answer I am getting excellent quality Dolby Vision on the Sony XBR65A9G coming from an Apple TV 4K box. With both Sony TV and the Apple TV box supporting Dolby Vision, the Apple TV box appears to up-convert all signals to Dolby Vision (even older SD black-and-white streaming media). I find the signal quality much better than the same media processed by a native app on the Sony TV.
However, there are several steps necessary to achieve this high quality Dolby Vision. The most important is to connect Apple TV 4K both to the Sony TV using an HDMI 2.1 cable, supporting up to 48 Gbps transfer rate. The Dolby Vision signal involves transfer of much more data. A slower speed HDMI cable cannot properly support such transfers. Also, be sure the Sony TV's External Input channel is set to Enhanced Format (Settings >> Watching TV >> External Inputs >> HDMI Signal Format).
On the Apple TV 4K box, make sure Settings >> Video and Audio >> Video - Format is set to 4K Dolby Vision.