I think you missed the point here. By virtue of being proprietary and owned by Microsoft, windows can not be de-microsofted.
By spending 30 seconds on the AtlasOS website, you can find that the first thing you see is "A modification of windows, designed for gamers". AtlasOS is only a modification of a Microsoft owned Windows operating system.
Anything else > AtlasOS > Windows
All good, I think we are coming from the same perspective. I misinterpreted the use of de-microsofted, I think with the context you are using it, it means to move away from Microsoft as much as possible within the WindowsOS, and the way I interpreted it was to totally rid Microsoft from Windows (which is not possible from my perspective).
AtlasOS looks like a step in the right direction, but I think there are alternatives which move further away from Microsoft (I.e linux). But I understand that some people just aren't looking to move that far.