I’m probably the wrong person to talk to with regards to getting a setup running with Linux, my entire setup, server and all clients are Windows. I’ve played just enough with Linux to know LVM snapshots need space to work, so the LVs don’t fill the PV, I also know that that’s not how e.g. the Debian installer sets LVM up, it fills the space with logical volumes & thus breaks snapshots.
I know UrBackup can also work with dattobd, which involves going & grabbing that from the project page since it’s not in the Debian repos, & Debian is pretty much all I’ve played with in recent years.
Again, given my experience with Linux & UrBackup being basically non-existant, short of apt purge & try again I’m at a loss where any remains that might interfere might lurk.