I'm not sure if these are the absolute best numbers, but this shows Windows at ~76% market share for desktop OSes. I've seen other numbers that have them at 66%. MacOS is the second place. Linux is third.[0]

The consumer market both does and doesn't matter to Microsoft. There are certainly more options besides Windows for the average person looking to buy their next device (assuming they'll even get a full desktop/laptop computer) and that will continue to be the case moving forward. If you look at what drives most of MS's decisions on Windows, business-wise, it's not a desire to capture more of the consumer desktop market. It's a desire to maintain the enterprise and to use that as a jumping-off point for more revenue-earning opportunities like 365 or Azure. They know they are far, far safer there and have the connections with clients that matter. Your CTO will not be throwing together a slide deck to justify spending a large slice of the budget on switching away from Windows, at least not anytime soon, because it means throwing out a lot of other stuff like Active Directory, SharePoint, and the like that no one wants to think about.

[0]https://gs.statcounter.com/os-market-share/desktop/worldwide...