Do you, as the client, have the ability to set what paths on your computer are backed up? If so, then you can install something on your client computer like Cryptomator. https://cryptomator.org/ This is free and open source software, available for Windows, Linux and Mac.
This software was designed for protecting things that get uploaded to the cloud, but it would work for your backup scenerio as well. What it does is maintain two directories of your stuff. One directory is open and unencrypted, the other is an image of it, except encrypted. Every change you make in the unencrypted directory is automatically reflected in the twin encrypted directory. What you would do is tell UrBackup to NOT backup the open/unencrypted directory, but DO backup the encrypted copy of it. This is why I originally asked if you, as the client, have the ability to specify what on your computer gets backed up and what does not. If your UrBackup server administrator has reserved this privilege only for him/herself, then you’re out of luck since you can’t set your own backup paths.