Local disk credentials issue

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Welcome to the forum @oneiro

Advanced destination options lost when editing a job in the web UI #4748 might be related.
You can add auth-password and auth-username on Options screen 5 instead, but first…

Topic title Local disk credentials issue isn’t what these are for. They’re mainly SMB.
Although Windows does the connection, sometimes it needs the credentials for the server.

Local folder or drive

  • --auth-password The password used to connect to the server. This may also be supplied as the environment variable AUTH_PASSWORD.
  • --auth-username The username used to connect to the server. This may also be supplied as the environment variable AUTH_USERNAME.

For truly local use (e.g. NTFS ACLs) Duplicati runs with the credentials that it’s started with.
Does that fit the behaviors you’re seeing? Sometimes one might want it run as an elevated
Administrator, which sometimes means an annoying UAC prompt, but that’s Windows’ way.
Alternatively you can run it as a Windows service as SYSTEM or whatever user you choose.
A service is most easily set up before starting to backup, but there are also migration guides.

Migrating from User to Service install on Windows (v3 is the latest version of migration steps)
What is the objective anyway? You seem to have credentials plans in mind, but what exactly?