Does the MacBook Air with M1 (or M2) actually support 10bpc on the 6k Display? It is never mentioned in the specs about the Macbook Air, AFAIK. My guess is that it does not. The M1 from 2020 also did only support 8bpc on the internal display.
For the MacBook Pro with M1 Pro it is explicitly mentioned in the tech specs that it supports 6k with 10bpc.
> Simultaneously supports full native resolution on the built-in display at millions of colors and: One external display with up to 6K resolution at 60Hz
My impression was that Apple implemented Thunderbolt themselves (and got rid of external chips) and that at least the first generation M1 machines lacked the 10bpc feature in the GPU and/or the Thunderbolt part.
When looking at a 16-bit PNG of a white to black gradient, I'm not able to visually spot any banding even when zooming in. It's fairly easy to spot steps when looking at a 8-bit PNG version of the same gradient. But the same happens on the built-in display despite it supposedly having only 8-bit color ("support for millions of colors").
Yeah, that's definitely my experience, too. It is difficult to actually get color depth information. Several other Macs, especially the older ones tell you there the color depth.
You might want to try out SwitchResX and see what it says about the screen. In some menu, there is color depth information about the screen. But I don't know if it is actually accurate and where the application gets this info from.
For the MacBook Pro with M1 Pro it is explicitly mentioned in the tech specs that it supports 6k with 10bpc.
This page claims that even the M1 MacBook Air from 2020 supports 10bpc on the external 6k monitor: https://support.apple.com/en-us/HT210437
But the actual technical spec page for the machine never says it, AFAICS.
https://support.apple.com/kb/SP825?locale=en_US
> Simultaneously supports full native resolution on the built-in display at millions of colors and: One external display with up to 6K resolution at 60Hz
My impression was that Apple implemented Thunderbolt themselves (and got rid of external chips) and that at least the first generation M1 machines lacked the 10bpc feature in the GPU and/or the Thunderbolt part.