Index except partitioned field not work

[ryzencool]

env

postgresql 12

Problem

I create a table like

create table cycle_flow (
   id serial8 primary key not null,
   order_no serial8 not null default 0,
   order_time timestamp not null default now()
)

create index on cycle_flow(order_time, order_no)

when i

select * from cycle_flow where order_time = ### and order_no = ####

and explain analyze. I found that index order_no not work and the scan is seq not index except i create index on child table manually .

Did i use pg_pathman incorrectly ? or not support create index on child tables automaticly?

What should i do make index order_no work?

Thanks.