Note that CSS Color Module Level 4 is still at the Recommendation Draft stage, and "supports" here is more accurately stated as "supports, except for Microsoft Edge (chromium) and Pale Moon (goanna)":
https://caniuse.com/css-lch-lab is probably a better resource for support, and it notes that the main layout engines all supported it earlier this year, and gives an estimated global support rate of ~85%.
sRGB/ProPhoto/DCI-P3 and HSL/HSLuv/Lch/Lab/OKLab are two distinct sets of functionality. The former defines the colorspaces (such as sRGB), the latter defines colors within a given colorspace. To see a visual demo of this, visit https://oklch.com/#70,0.1,165,100 and enable Show P3 and Show Rec2020; two additional thin white lines will be added showing the colorspace truncation points for the OKLCH color (70% 0.1 165).
https://caniuse.com/css-color-function tracks support for the colorspaces, complementing the above link for Lch/Lab, and showing essentially the same current data: All desktop and the two top mobile browsers now support it.
I'm really glad to see this. Thank you for sharing. That makes me much more optimistic about what will come of this.
(Note that all browsers are currently failing LCH and OKLCH tests 9 and 10, and Firefox failing 15% of the CSS Color v4 parsing tests, at https://wpt.fyi/results/css/css-color?label=experimental&lab... — but this is still a page full of great success for CSS Color v4! So happy.)
https://test.csswg.org/harness/results/css-color-4_dev/group...