What are they defining as an operation system? It’s a term that has fuzzy edges as a technical term, and given laws are usually piss poor at defining technical terms, I can’t see it being well defined in CA law.

I think there's a lot of proprietary stuff, from Google Play Services to Pixel specific features. A very significant stack of "modern" software layers are proprietary, even on Android.

So if you load AOSP and don't use Google Play Services, then you're exempt?

Sounds like another fellow GrapheneOS user!