You can try to use Seedvault to back up your data then restore that data on a new phone.
Seedvault isn't very reliable so it's very likely that Seedvault will miss some data. Make sure you back up as much as you can manually and be prepared to restore your data manually. Sorry for the trouble. The GrapheneOS team plans on replacing Seedvault in the future.
You can start a Seedvault backup in Settings > System > Backup and follow the instructions from there.