AOSP is Android without the Google proprietary stuff (and without the manufacturer proprietary stuff, e.g. Samsung's). If you install bare AOSP, it will look like the Android on a Pixel phone, but the biggest difference you will see is that it won't have the Play Services or some Google apps.

If you want to be a certified Android system (like all Android manufacturers do), you have to port AOSP to your hardware, install the Play Services as a system app (giving Google root access), install the system apps you want (e.g. Samsung have their own UI, maybe their own camera, their own store that they want to be installed as system apps), pass some conformity tests by Google (Google wants to ensure that it's good enough to be called "Android") and pay a ton of money to Google for the licence.

But as an individual, you can just download the AOSP sources, build them and install them on your phone. It's AOSP, but not Android.

GrapheneOS is based on AOSP. /e/OS is based on LineageOS which is based on AOSP. Those are not Android systems, they are AOSP-based systems. In a way like Linux Mint is based on Ubuntu which is based on Debian. Those are different layers. If you hate Canonical, it doesn't mean that you have to hate Debian, even though Canonical does contribute to software that runs in Debian (like the Linux kernel). The comparison is worth what it's worth, but I hope you get my point :-).