ICC profile is built-in in memory of my laptop screen?
Yeah. Surprisingly, nearly every display comes with somewhat accurate color information in its EDID.
Even Windows can't do it
Afaik they did actually implement something in this direction in Windows 11, but it's not exposed in a user friendly way yet.
There is no saturation slider, though. I've seen it on some screenshots.
It's currently always shown if the built in color profile, HDR or an ICC profile is used. IIRC it wasn't visible with the color profile in some older version of Plasma though, maybe that's why you don't see it.
Yeah, afaik MacOS can do it too.