how do I use jsonb_array_length with condition?

You need to unnest array elements with jsonb_array_elements():

select id, value
from t
cross join jsonb_array_elements(ss)
where (value->'approved')::bool

Use the boolean aggregate function bool_and to check whether all elements of an array has "approved": true

select id, bool_and((value->'approved')::bool)
from t
cross join jsonb_array_elements(ss)
group by id

Db<>Fiddle.

Read in the docs:

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