Prepared statements are currently not supported:
-PREPARE is5 AS
FROM GRAPH_TABLE (snb
MATCH (m:message where m.id = $1)-[au:hasAuthor]->(p:person)
COLUMNS (p.id, p.firstName, p.lastName)
) tmp;

Will return Binder Error: PREPARE has not been implemented yet for DuckPGQ queries

Seems a bit more tricky to implement than first thought. The implementation currently throws Binder Error: Unable to find DuckPGQ Parse Data