K8y
First of all, GrapheneOS adds a network permission toggle as a feature , which by itself improves privacy significantly: Now it takes two Apps with mutual consent to send data out.
The IPC already mentioned here is nothing intrinsically evil but an integral part of how Android works. If one wants to avoid it, apps can be furthermore isolated by separating them in user profiles - apps can only communicate with apps within the same profile:
Apps can't see the apps in other user profiles and can only communicate with apps within the same user profile (with mutual consent with the other app).
source: https://grapheneos.org/features#improved-user-profiles
This feature is not a unique GrapheneOS feature, but they have nevertheless further improved user profiles.
The developers of GrapheneOS seem to work hard on implementation of an IPC toggle, but this seems more difficult than expected - which the developers openly communicate, for example:
App Communication Scopes] will allow choosing which user installed apps can see each other and communicate with each other. It is very hard to implement properly and may not actually make sense as opposed to doing something like adding support for having multiple Private Spaces or something similar to that. Profiles already provide what is wanted and App Communication Scopes requires providing nearly everything profiles do...We started work on App Communication Scopes but it's unclear if the approach actually makes sense as opposed to providing better support for nested profiles than the existing work profile and Private Space features where they can only be used in Owner and you can't have more than 1 of each. Private Space UI could also be improved in various ways. We'll have to figure out what kind of approach actually makes sense. Lots of ways to bypass a basic App Communication Scopes feature. App Communication Scopes would be useful for attack surface reduction for apps within profiles even without exhaustively covering all ways apps can communicate. We haven't yet figured out how this should be approached as a whole.
source: https://grapheneos.social/@GrapheneOS/113973056128380064
Finally, the mayne somewhat inconvenient truth is that users also have to contribute if they wante more privacy - GrapheneOS improves privacy a lot but if a user decides to install all the privacy-invasive apps out there, GrapheneOS won't work miracles.