How do I see where postgres privileges are coming from for a role?
The permissions are stored on the individual objects, and there is no central view to see them all.
You could use the access privilege inquiry functions for each type of object to get that information.
For SELECT on tables, views, sequences, composite types or materialized views that could be:
SELECT oid::regclass, relkind
FROM pg_class
WHERE  has_any_column_privilege(
          'cloudsqliamserviceaccount'::regrole,
          oid,
          'SELECT'
       );

You need similar queries for other object types.
Note that such a query will only give information about objects in the current database, so you would have to run it on each database in turn.
Another crude method is to run
DROP ROLE cloudsqliamserviceaccount;

That will give you an error message and list some of the privileges the role has in the current database.