I worked on a project with similar requirements. I just serialized the data with protobufs, encrypted it, and stashed it in S3. It was sensitive data so this also had the advantage of being easy to secure and audit.
No point using a relational db for that kind of thing.
The problematic part with PostgresSQL JSONB is modifying a JSONB column content. In any case, we totally replace the old content by a new one. So, the update operations turn to the complex queries that can lose the content. You can avoid this by performing the full JSON reorganization before the persistent operation.
You still don’t have the richness of MongoQuery and the aggregation framework and the tooling around working with JSON data isn’t there. Let alone the native driver support.
No point using a relational db for that kind of thing.