What is the deal with the "invisible schema" pg_catalog?
It's not a schema in my database.

Yes, it is. And it's neither &quot;invisible&quot; nor undocumented:
Quote from the manual

In addition to public and user-created schemas, each database contains a pg_catalog schema, which contains the system tables and all the built-in data types, functions, and operators. pg_catalog is always effectively part of the search path.

All views and tables in the pg_catalog schema are documented here