Finally my adapter arrived. I was a bit anxious because of the problems others reported.
For me it works flawlessly on the theoretical maximum of the 1080TI (4k/120Hz/422/10bit HDR). Switching in/out of HDR, and changing resolutions works smoothly. Even when changing in-game.
One weird limitation: 120HZ only allows 422 colors, no matter the resolution or bit-rate. This might be a limitation of my TV, or some missing EDID in the adapter. At 60HZ, RGB/12bit or YUV444/12bit is possible.
Because 1080TI does not have DSC, 444/12bit is not possible, this is a known limitation.