How does solid achieve a high level of interoperability and how does this improve or enhance data ownership/privacy ?
Solid by itself doesn’t mandate a particular data model (it couldn’t, since the number of potential applications is unlimited), so it’s up to app developers to agree on a shared data model. Solid can provide mechanisms for developers to enforce that agreement among them, but that’s still being fleshed out here: GitHub - solid/data-interoperability-panel: Repository for the Solid Data Interoperability Panel
The interoperability by itself improves data ownership because your data isn’t necessarily locked in to one developer’s app. It doesn’t by itself enhance privacy - that’s more the result of being able to choose who to trust with hosting your data (or doing it yourself) and who to share it with.