I don't think you understand how different Android and Linux distributions truly are.

Linux alone refers to the kernel. There are custom AOSP kernels based on the Linux LTS versions with a few extra patches but that is basically all that connects Linux to Android.

But absolutely everything in userland is wholly diifferent in Android than with any Linux distribution out there.

And you can't just replicate what Android did on top of the Linux kernel without Google amounts of resources. Which GrapheneOS does not have in the slightest.