Workaround: Apple TV video settings reset to defaults on power cycle

Sharing a workaround/solution for the benefit of others.

I had an issue with my new Apple TV 4K (3rd gen running tvOS 16.5) "forgetting" video settings after turning my TV off/on via the Apple TV remote. In particular, I've been trying to set either YCbCr w/ 4:4:4 chroma or RGB output to fix artifacts in some logos and UI elements in the menus. These options work, but always reverted to YCbCr w/ 4:2:0 chroma subsampling on a power cycle.

After some back & forth with Apple support, they identified the issue was due to my TV briefly advertising HDMI 1.4 EDID (with support for only 4:2:0) on startup, before advertising support for full HDMI 2.0. The Apple TV thinks it's been moved between TVs, so it reverts to safe defaults.

In my case the TV has an option for the advertised HDMI EDID between 1.4 / 2.0 / Auto. 2.0 and "Auto" both exhibit the buggy behaviour (advertising 1.4 then 2.0), presumably . Counter-intuitively, the workaround was to choose HDMI 1.4 EDID. The TV doesn't advertise support for 4k60 4:4:4, but the Apple TV allows this to be overridden. As the TV no longer switches between 2 EDIDs on startup, the Apple TV no longer clears the overridden settings for safety.

Hopefully this helps someone.

Possibly related to:

Default video format keeps changing rando… - Apple Community