Can I directly call Greenplum functions using Postgre extensions

When I write the following code in DuckDB:

CREATE SECRET ps (
TYPE postgres,
HOST '${ip}',
PORT ${port},
DATABASE ${dbname},
USER '${user}',
PASSWORD '${password}'
);

ATTACH 'dbname=${dbname}' AS gp (TYPE postgres, SECRET ps);

CALL postgres_execute('gp', 'SELECT * FROM gp.dw.getcombinesn(''HF52RT0006'')');
I encounter the following error:

ERROR: cross-database references are not implemented: gp.dw.getcombinesn
Is it possible to directly call Greenplum functions using the Postgres extension in DuckDB?