@drwtsn32 is correct, there is no built in support for centrally handling multiple installations, though there is dupReport from @handyguy:
If you’re looking for central MAINTENANCE, not just reporting, since Duplicati uses a web interface you could always port forward (SSH), VPN, or remote into the various machines to access individual configurations. While it’s technically possible to expose the Duplicati web interface to the internet, it wasn’t be hardened or tested for that type of use so could be insecure.
In theory somebody could start a GitHub topic or Bounty for hardening of the GUI or securely exposing CERTAIN functionality via an API…