Включив логи стало ясно, что pgAdmin4 тянет это дело вот таким запросом:
SELECT
pr.oid, pr.proname || '()' as name,
lanname, pg_get_userbyid(proowner) as funcowner, description
FROM
pg_proc pr
JOIN
pg_type typ ON typ.oid=prorettype
JOIN
pg_language lng ON lng.oid=prolang
LEFT OUTER JOIN
pg_description des ON (des.objoid=pr.oid AND des.classoid='pg_proc'::regclass)
WHERE
proisagg = FALSE
AND pronamespace = 2200::oid
AND typname IN ('trigger', 'event_trigger')
AND lanname NOT IN ('edbspl', 'sql', 'internal')
ORDER BY
proname;