There are 3 folders that need to be backed up in the official install. In the bitwarden_rs install, the default docker setting will have all 3 of these folders in same location: /data/.
Backing up this one folder will backup your sqlite database, key files and attachments.
Note that the official bitwarden install uses a MySQL database which is automatically backed up nightly. This is not the case with the bitwarden_rs. Instead you should use a backup program to create incremental backups.