Currently, Apple TV 4K auto-configures those outputs during the set-up stage. Apple claims that this helps to avoid the irksome jittering that plagues some TVs when they switch in and out of HDR modes. The company's solution is to strong-arm the best video setting for your set. So, if the Apple TV sets to output 4K Dolby Vision HDR, it will carry on displaying that format, even if you switch to a video made for standard dynamic range and standard definition. You can still force the Apple TV to display specific resolutions and refresh rates, but you'd expect a modern (not to mention pricey) set-top box to better handle itself.
In the near future, it will. With tvOS 11.2, Apple will introduce a new "Match Content" setting within the device's audio and video menu. It will essentially put you in control of the video output, allowing you to choose to match the dynamic range and refresh rate -- although, both will be disabled by default. There's no ETA on when the update will arrive, and Apple warns that it will only work with "compatible apps." But, as long as it fixes the issue at hand, customers should be pleased. Then, the only thing missing from the stellar device will be Dolby Atmos support.