Which one? Android SDK source is under Apache licence, but binaries are under EULA. There were some efforts to properly package it under free licencje, but currently no one do it.
As for Android being giant blob, maybe not the best word but it really is barely available to change. If I want to add a new feature to the UI, I need to build whole ROM again and deal with Google’s developing platforms. While on Linux you can get the code for a component from some GitHub/Codeberg and modify/reinstall just that component.