GrapheneOS includes an encrypted backup system covering far more data than Google cloud backups. It backs up data for apps opting out of cloud backups with allowBackup="false" since it operates in the device-to-device transfer mode. The backup system supports arbitrary sync services with a compatible API. Backups are per-profile so you can test it by restoring to a secondary user.
We plan to entirely overhaul the backup system but it already works fine. It could be a lot simpler and cleaner both in terms of implementation and user experience. We're in the process of overhauling the other apps first but we'll get to it.
One clarification:
> It backs up data for apps opting out of cloud backups with allowBackup="false"
This is untrue for older apps targeting API 30 (Android 11) and earlier. As I understand it, allowBackup is still respected for them, preventing their backup even in D2D mode. https://github.com/GrapheneOS/os-issue-tracker/issues/1112#i...
Those apps are slowly going extinct since the Play Store stopped accepting updates written against the older SDK in 2022, but I gather there are still a few floating around out there (including some niche favorites that have unfortunately abandoned development).
And one wish:
I'd love the ability to maintain a "hotspare" device that's identical to the original in every important way. So if your phone is chucked in the ocean, dropped down a cliff, etc. you can just grab the other one (checkpointed from a few hours or a day ago) and seamlessly keep on going.
I think this is impossible today because of the way the system protects secrets in the Android Keystore and how it's intertwined with the TEE / secure element / Titan M2 / etc. I wish there were a way to truly own my phone including the ability to perform perfect-fidelity backup and restore.
thanks for chiming in.