Backup Apps data to SMB share

I have a decent enough server with plenty of compute/ram/storage. I also have a synology with 90 odd TB.
I currently have proxmox on the server, running a variety of VMs and LXCs, and a Windows VM on the synology, with tons of disk, an SMB share, proxmox does a backup of all those VMs and containers to that SMB share. The windows machine then does a backup to Backblaze. Its not lightning fast, but it doesn’t need to be, but it only costs $9 p/m, regardless the amount of data (currently around 12TB).
What I would like to do is move to Truenas EE (not on to of proxmox, I’d do a new install), run the apps I want there (Immich is a biggie for me so will use that as an example), where all the Immich data (photos) are backed up to that windows PC across the network, and then gets sent to BB.
Replications methods don’t really appeal, I don’t need realtime, and I don’t want to go Linux (I struggle, I’m a Windows guy).
Can anyone suggest the best way to do this in EE? Is it even possible?

I’m looking, and at first glance perhaps syncthing might be the answer. I’ll try over the next few days - unless someone else can save me some time by saying it won’t!

Syncthing should work - you need to make sure that you configure it to sync one way.

An alternative is SyncBack Free - but that would be a pull from the windows system rather a push from TrueNAS.