alt Hacker NewsAndroid is closed-source but with some open-source components, for only some of which they'll actually follow the license and give you the source code.
Android is closed-source but with some open-source components, for only some of which they'll actually follow the license and give you the source code.
AOSP means "Android Open Source Project". You can get the sources of Android, modify them, and build the whole OS. The Android SDK is open source as well.
GrapheneOS is based on Android precisely because Android is open source. They couldn't do that with iOS, or Windows, or any proprietary OS. Same for LineageOS.
Honestly it seems like you don't really know what you are talking about here?