Database backups are part of Managed databases – that is also where you’ll find instances, additional users and imports from existing databases.
How volume snapshots and restores work in detail is covered under Volumes & snapshots; rolling back to an earlier version under Deployments.
What gets backed up when a customer leaves is described under Tenant pipelines.
Whether a crash is really over after a restore is shown by the logs of all instances under Logs & monitoring; what Helm charts do with their disks is covered in the post Helm charts and their disks.