http://uwb25d43nnzerbozmtviwn7unn7ku226tpsjyhy5n4st5cf3d4mtflqd.onion/posts/grapheneos/index.html
You can't trust the corporate options, and they're the easiest way for the police to access your data. If you must back up your phone, back it up to your encrypted computer. GrapheneOS currently offers Seedvault as a backup solution, but it's not very reliable. As the documentation notes , connecting directly to a computer requires "needing to trust the computer with coarse-grained access", so it is best to avoid it.