I don’t have any hard numbers, only what I have seen out in the world. But a good number of POS systems, embedded things like MRI machines, tire balancers in mechanics shops and ATMs run some flavor of embedded Windows.
It is not nearly as huge as *nix is, but it is not exactly uncommon either.
The fuckery Microsoft has been doing with trying to outright trick people into signing in to the OS with a Microsoft account and using things like OneDrive combined with just how good Proton has gotten pushed me to make the switch full time a year or so ago for my personal usage.