I have a synology NAS where I backup my photos to. What would be the most cost effective way to encrypt and back up this data without having to purchase another NAS and install it at a family member's house. It would be about 5 TB and would not touch the data unless my NAS completely takes a crap.
Hetzner.com Storage Box might be worth looking into. I have no personal experience with it yet but I'm considering it.
5TB is about 13€/month. You get 20 Snapshots for data safety. It supports a lot of protocols like cifs and rclone which makes it possible to mount as a network drive and encrypt remote backups with rclone crypt.