PostgreSQL equivalent to MongoDB's Mongoose?
It depends on what you are coding in. Mongoose is an ODM or object data modelling tool for Node.js.
Those object modelling tools are typically tied to a particular language or framework. In Java, one might use Hibernate. In Django, there is a custom ORM (swap data for relational). With Node, one might use a tool like Sequalize.
Sequalize is probably the answer you are looking for.
If you are looking for a way to convert JSONB typed columns into objects that you can load update and save like you do using mongoose:
The ยง "JSONB (PostgreSQL only)" type in the sequelize documentation will show you how.
node-postgres might be an alternative