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.
AtlasOS is great wish I discovered it before doing it all manually. All it really does is apply group policy changes and config management, which is what any enterprise workplace will do by default. I have 15 years experience as a sysadmin in a mixed OS environment in the operation of critical infrastructure. We're bound by intense regulations and audited often, and Windows is the workstation OS that we can easily manage security-wise. This is in contrast to the notion of Windows as a garbage consumer product, which yeah not wrong there, but people might not be aware of it's compliance with industry standards and security regs. Which is a shame because that's ultimately what's evil about the MS approach to business, they create a problem for businesses and offer the solution.
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.