A wrap-up of what I ended up doing:

• Replaced the bare metal Ubuntu with Proxmox. Cool cool. It can do the same stuff but easier / comes with a lot of hints for best practices. Guess I’m a datacenter admin now
• Wiped the 2x960GB SSD pool and re-created it with ZFS native encryption
• Made a TrueNAS Scale VM, passed through the SSD pool disks, shared the datasets with NFS and made snapshot policies
• Mounted the NFS on the Ubuntu VM running my data related services and moved the docker bind mounts to that folder
• Bought a 1Gbps Intel network card to use instead of the onboard Realtek and maxed out the host memory to 16GB for good measure

I have achieved:

• 15min RPO for my data (as it sits on the NFS mount, which is auto-snapshotted in TrueNAS)
• Encryption at rest (ZFS native)

I have not achieved (yet…):

• Key fetch on boot. Now if the host machine boots I have to log in to TrueNAS to key in the ZFS passphrase. I will have to make some custom script for this anyway I guess to make it adapt to the situation as key fetching on boot is a paid feature in TrueNAS but it just makes managing the storage a bit easier so I wanna use it now. Disabled auto start on boot for the services VM that depends on the NFS share, so I’ll just go kick it up manually after unlocking the pool in TrueNAS.

Quite happy with the setup so far. Looking to automate actual backups next, but this is starting to take shape. Building the confidence to use this for my actual phone backups, among other things.