I could imagine a LibreWindows where all the bloatware, advertising, microsoft backdoors and so on are completely removed from the source.
Russia is funding ReactOS.
ReactOS is not based on Microsoft source code. It's a clean-room reimplementation and anyone who has ever looked at Microsoft code is permanently banned from contributing to that project.
How do they know that their contributors never took a look at Microsoft source code?
This was a major factor in the Oracle v. Google case, where some of the argument boiled down to "well, how else would you do that?".
ReactOS audited their code and showed that none of it was Microsoft's.