I have an HDD at my parents place and manually bring over snapshots when I visit. Off site does not necessarily mean cloud.

If you are using aptitude (apt) it is quite simple: https://ubuntu.com/server/docs/how-to/software/automatic-updates/

If you just want security updates and are fine with the default configs:

# apt install unattended-upgrades

I don’t know why you are being downvoted. You are right, Syncthing does not support local sync.

From the changelog:

Packaging

• Debian Bullseye and Ubuntu Focal packages are no longer built

Are you maybe running Focal?

Not free, but Brics CAD oficially supports a few distros.

Something went wron with that link.

I assume fo collaboration and such.

Tbh I still consider Proxmox as Debian, so you’re pretty much there ;).