Put it on a zfs dataset and back up data on the filesystem level (using sanoid/syncoid to manage snapshots, or any of their alternatives). It will be much more efficient compared to all other backup strategies with similar maintenance complexity.
Filesystem backups may not be consistent and may lose transactions that haven't made it to the WAL. You should always try to use database backup tools like pgdump.
Entire companies have been built around synchronizing the WAL with ZFS actions like snapshot and clone (i.e. Delphix and probably others). Would be cool to have `zpgdump` (single-purpose, ZFS aware equivalent).