The difference between custom windows builds and GrapheneOS is that one is buggy and broken and the other isn’t. Probably because Windows is proprietary and not designed to be modified, unlike Android.
Also yes, you can modify AOSP and call it a separate OS. Plenty of other projects have done so in the past.
crystal@feddit.de 1 year ago
Would you not call Ubuntu a different OS than Debian? And if you do, would you find it unreasonable to say that Ubuntu offers Debian app compatibility?
GrapheneOS and stock Android have a similar relationship.