Welcome to the forum @rayalot
I don’t follow that. Something else is making backup that Duplicati will back up again?
Many people run Duplicati as root. LinuxServer.io image tends to run very restrictively.
Duplicati image used to run only as root, but is getting enhanced to allow UID controls.
EDIT 1:
If you want to see Duplicati user from its GUI, see About → System info → UserName.