Unable to migrate from postgres-13 to 14

Hi,

I am trying to migrate my database from postgres-13 to 14 but getting following error:

pg_restore: error: could not execute query: ERROR:  function array_append(anyarray, anyelement) does not exist
Command was: CREATE AGGREGATE "public"."mode"("anyelement") (
    SFUNC = "array_append",
    STYPE = "anyarray",
    INITCOND = '{}',
    FINALFUNC = "public"."_final_mode"
);

To work around this problem I decided to drop this aggregate in postgres-13 and create it again with the supported version of array_append in postgres-14.

But when I tried to drop it in postgres-13 I got following error:

#drop aggregate mode("anyelement") CASCADE;
ERROR:  cannot drop function mode(anyelement) because it is required by the database system

I don't understand  why the database system is using my user defined aggregate. If it is a system defined aggregate then it should not be copied from postgres-13 to postgres-14. It should be there in postgres-14.

Please suggest some work around.

Thanks,

Jasvant