If MS Windows is AI-generated, can it still be under copyright?

Microsoft has claimed that something like 30% of the code for Windows is AI-generated. (I have not verified that they even said that, maybe that's totally fake.) Last i checked AI-generated stuff cannot be copyrighted. Does this mean that significant portions of Windows are un-copyrightable, and MacroSlop couldn't do a damn thing if someone leaked those parts?

And then, reservations about including slop in a software project aside, what could this mean for things like ReactOS? They've been careful to avoid including any MS-owned code, but nobody owns slop code.