One way that you can do this is just to zfs replicate a volume to another system that has an encrypted zfs mount. Probably not what you are looking for, but voi

One way that you can do this is just to zfs replicate a volume to another system that has an encrypted zfs mount. Probably not what you are looking for, but voila - end to end snapshotted encryption - except it's not a "backup", more like a hot failover volume.