postgres=# ALTER DEFAULT PRIVILEGES IN SCHEMA my_schema REVOKE EXECUTE ON FUNCTIONS FROM PUBLIC;
ALTER DEFAULT PRIVILEGES
As the documentation explains:
Default privileges that are specified per-schema are added to whatever the global default privileges are for the particular object type. This means you cannot revoke privileges per-schema if they are granted globally (either by default, or according to a previous
ALTER DEFAULT PRIVILEGES command that did not specify a schema). Per-schema REVOKE is only useful to reverse the effects of a previous per-schema GRANT.David J.
