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.

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

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.