Words sound unsure. Do you mount it? rclone mount? How and when? What options? Not our area.
Closer to our area, but what does it have to do with the mount? Rclone backend doesn’t need mount.
sounds consistent with the rclone manual about Config:
--config string Config file (default "$HOME/.config/rclone/rclone.conf")
and
Maybe pass rclone option into Rclone backend?
--rclone-option (String) Options will be transferred to rclone.
There are other ways to try it, e.g. force root Duplicati’s $HOME to yours. That likely moves databases.
You could also make a symbolic link so root rclone config winds up actually going to your rclone config.
EDIT:
If you go with the Advanced option, and it goes away on next Edit, try putting it on screen 5 instead of 3.