What version of Password Safe does Strongbox support?

Strongbox supports version 3 of the Password Safe format. In particular it implements version 3.31, though not all features maybe supported or exposed in the UI. In particular Linked entries, Credit Card fields and other less used features are not supported, though Strongbox will respect that data and not edit or change it. So your data is always safe, it’s just that Strongbox does not display it in the interface.