Update jsonb set new value select from the same table - postgresql

Question

i have a table foo:
id | items
---+--------------------------------
1 |{"item_1": {"status": "status_1"}}
2 |{"item_2": {"status": "status_2"}}
...
I need to update all rows in column items which is a jsonb and set after {"status": "status"} new values ("new_value": "new_value") and after update the result must look like this:
id | items
---+------------------------------------------------------------
1 |{"item_1": {"status": "status_1", "new_value": "new_value"}}
2 |{"item_2": {"status": "status_2", "new_value": "new_value"}}
...
i've tried to do this:
WITH result AS (
INSERT INTO foo (id, items)
SELECT id, options || newvalue as res
FROM foo AS bar,
jsonb_each(bar.items::jsonb) AS item,
to_jsonb(item.value) AS options,
jsonb_build_object('new_value', 'new_value') as newvalue
WHERE id IN ('1', '2'...)
ON CONFLICT (id)
DO UPDATE
SET items = foo.items || Excluded.items::jsonb RETURNING *)
SELECT item.key AS itemkey
FROM result AS res,
jsonb_each(res.items) AS item,
to_jsonb(item.value) AS options;
but when i run this script the postgres shows this error message:
on conflict do update command cannot affect row a second time postgres
i dont understand what am i doing wrong?
UPDATE#1
Postgres version 9.6
table foo id = TEXT UNIQUE NOT NULL
about why INSERT but not just UPDATE? the answer is this is my mistake first mistake.

Answer 1

after some reading postgres functions finally i find out:
UPDATE foo as t
SET items = result.new_value
FROM (SELECT st.id, new_value
FROM foo AS st
CROSS JOIN LATERAL (
SELECT jsonb_object_agg(the_key, the_value || '{"new_value": "some_new_value"}'::jsonb) AS new_value
FROM jsonb_each(st.items) AS x(the_key, the_value)
LIMIT 1) AS n) AS result
WHERE result.id = t.id;