The nearest thing is an interrupted backup is marked “partial”. “incomplete” doesn’t really fit “broken”.
One also can’t really identify which backup version is incomplete because the new ones build on old.
That’s the list-broken-files that you tried, unfortunately finding it stopped by some deeper problem.
Few people want deep information, but the contents of the database are described. How the code gets there is described in the code though. FWIW, here’s some developer-level documentation on database:
Developer documentation
Documentation for the local database format
Is there an ER Diagram and Data Dictionary?
Database rebuild
So would we all, but until some people from the community skill up and dive in, all we can do is hope.
As a free community project, Duplicati only exists and perhaps improves thanks to volunteers helping.
There are lots of openings in development, documentation, test, forum, etc. Thanks to those who help.