There is no evidence that any CX can do 1080p/120Hz 4:4:4 chroma or 4k/120Hz 4:4:4 chroma. It downsamples to 4:2:2. You can test the 1080p/120Hz mode with most newer PC sources. 4k/120Hz can be tested with any PC with a Turing card using the Club3D adapter. 1440p/120Hz is the only mode in the EDID with >60Hz refresh rate that supports 4:4:4 chroma.
RTings explains how to test here:
Chroma Subsampling: 4:4:4 vs 4:2:2 vs 4:2:0https://www.rtings.com/tv/learn/chroma-subsampling
At this time, we need evidence that the CX
can do 4:4:4 in either of those modes, not that it can't. If you have a HDMI 2.1 source and a CX and have been able to make 4:4:4 chroma appear (not just be listed as RGB input), please provide pictures.