Is this the same question as was asked 26 minutes earlier at Please i have a question, but maybe wasn’t answered until this one was posted? Regardless, what changes from there were tried, and how did it go?
One addition I’d make is that if you don’t install as service (which takes some setup), it’s not simply use of Windows account that’s “Administrator” (as opposed to “Standard User”), but the Duplicati shortcut needs “Run as administrator” checked in Right-click --> Properties --> Advanced, then a UAC prompt each start.
Or if you prefer a service install (which has other benefits and challenges), here are some resources on it:
Forum How-To Migrating from User to Service install on Windows gives some info on how you can do that.
Duplicati Tutorial 02 Install Duplicati as a Service is a video that I think would also give an idea of the steps.
Service installs are more work, may be less common, and can be more troublesome than a regular install.