Say I have Google Camera installed with network permissions revoked. Say I also install Play Services which does have network access. Would Google Camera be able to share data about my pictures to Play Services which would then phone home to Google?
I don't know if Google Camera would share the information with Sandboxed Google Play. However, something to be careful of, is if you have two apps by the same developer (Google in this case), and you have network permissions for only one of them. The developer could share those permissions with their other app. TheHatedOne did a podcast episode on this. He checked with a GrapheneOS developer beforehand, and found, that this is possible.
Yes. Apps can consensually trade information. So if play services is connected to the network, it can share information it receives from other apps.
The only way to isolate an app from communicating is to put it in its own profile either a work profile or a secondary user.
Simply disabling network access does not prevent the app from talking to other apps that do have network access. You need to be careful based on your threat model
This is why I don't like Graphene os. Its encourages using proprietary apps that over Foss. With a Foss camera app from F-droid you don't need play services and the app with do exactly what its meant to do, nothing more.
I'd like to see some evidence that F-Droid is less secure (or privacy respecting) than using the big Gs playstore or services, which many, if not most, playstore apps depend on to function.
I mean this sincerely and respectfully. I'd love to look onto it.
Because in my current opinion and approach, if you vet your apps and practice good digital hygiene, then FOSS>GOOGL/Alphabet for nearly everything from a privacy and security perspective.
Edit: if I misunderstood and you were saying don't use G playstore or Aurora AND don't use F-Droid, then may I ask where are you getting your apps, other than directly from the devs page or github and so on?