Well I can't tell you what the right choice in your system is, but in the general case I think going with a relational model by default generally makes sense because it's rather future proof. By that I mean a relational model gives you the most flexibility in the future to evolve your system in ways you couldn't/didn't anticipate when the system was initially designed.

No point using a relational db for that kind of thing.

Not to mention the LINQ driver....

And you can’t do updates on individual JSON fields in Postgres.

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.

Anything that you can store in object database you can normalize and store in an RDMS. ORMs have been translating relational models back and forth to object models for decades.

In the case of Mongo, you just create one object containing other objects, lists, arrays etc and the driver serializes it to a JSON like structure and stores it as is in the collection.

In the case of an RDMS, you create your C# classes to model your tables and relationships.

The driver translates the LINQ to the appropriate query language.