Blooey thank you, it's very helpful.
deepflame this is great! I'm glad to hear it's working for you. Re. iOS, I don't see why a similar solution wouldn't work if indeed dithering is toggled via the same mechanism. We just need to get there. I think @DisplaysShouldNotBeTVs is working on something.
asus389 this is the million dollar question. Waiting for someone with a true 10-bit display to try it out and measure things. If it indeed turns off dithering in response to a 10-bit panel, that would be amazing. In fact, you don't even need a 10-bit display, TRUE 8-bit (which seems tricky to find also) with Stillcolor should suffice.
jordan which ViewSonic model is that? They released a new VX2781-4K-PRO-6 with IGZO IPS panel in China a few days ago which claims to be true 10-bit!
madmozg the mechanism is the same across all M-series Macs. It disables the enableDither property and with that the GPU/DCP stops applying temporal dithering to the pixel buffer. Try using an sRGB color profile and see if that makes an additional difference. Did you enable Launch at login? The app needs to run every time the computer starts.
NewDwarf @Blooey explained it very nicely. The main thing to note is that Apple's GPU/DCP applies temporal dithering to the pixel buffer way before it even touches your HDMI/Thunderbolt port. That's why you can capture all of this with an HDMI capture card.