That’s not a command, it’s an option for a missing command. Please type command and options.
An easy way to set this up and not have accidents of missing options is to set up in the GUI, then Export As Command-line, or if you already have a full command, add the option onto current ones.
If you might ever use the GUI, e.g. instead of a CLI restore command, keep the setups compatible.
True CLI (as opposed to GUI Commandline) is independent of GUI and needs all settings supplied.
I was trying to add this configuration not to the backup jobs themselves but as one the default options for Duplicati as a whole, as if when in the UI selecting settings on the left and then setting the configuration under default options.