many years ago i wrote a gtk3 prototype to output 10-bit colour through cairo and x11 (that’s what dt is based on). it was very hard indeed to teach cairo 10 bits. it was either secretly doing 8-bit (you could tell by banding in gradients) or it was very slow. like 30sec for one refresh. i don’t know this has changed in the mean time, my guess is that efforts would rather have gone into gtk4+friends.
i’m now using vulkan for my image processing, that does support true 10-bit output. with dithering enabled in 8-bit, i cannot attest that 10-bits make much of a difference to my old eyes.