I feel confident in guessing that any net changes in Windows popularity have close to no relation to Microsoft's policies around trusted CA. The number of users who are worried about sketchy certificates being trusted by default are dwarfed by the number of users who don't have any idea what a "trusted CA" is but care about more "visible" things like UI changes, performance, and how hard Windows is pushing Edge and other things they don't want.

I looked at the graphs at Statista. I don’t think it’s so clear cut. Mobile OSs have pushed it down, but it seem to dominate PC market. Do you have a graph that shows its decline on computers, not mobile phones? Or in absolute unit counts?

You need to show statistics to prove that, not just throw the statement out there, possibly only based on the vibes on HN.