If you are asking about ways to get backup reports, maybe some of these will help. If not, could you clarify?
Duplicati-monitoring.com - central monitoring of multiple Duplicati instances + nice email reports
Announcing dupReport - A Duplicati Email Report Summary Generator
The first link has the fairly simple outputs Duplicati can make. The other two third-party tools build on them.
A web API does exist but is mainly for browser GUI code to have the raw input/output interface that it needs.
Duplicati Client is a third-party command-line client that uses the same API, for those who need such a tool.
The databases certainly contain information, but the wrong sort of access could interfere with Duplicati use.