It's a bit more nuanced than that. PostgreSQL supports JSON/JSONB data types so if you need, you can use it in a way similar to MongoDB, with less structure and

It's a bit more nuanced than that. PostgreSQL supports JSON/JSONB data types so if you need, you can use it in a way similar to MongoDB, with less structure and the remaining caveats, but with transactions and all other goodies working out of the box and being able to use standard RDBMS features if needed.