Could you post desired output you are looking.
What happens when different users document has some userid =1, same for the other documents. What is desired output
SELECT users, contacts, banks
LET users = (SELECT RAW u FROM default ud UNNEST ud.users AS u WHERE u.userid = 1),
contacts = (SELECT RAW c FROM default uc UNNEST uc.contact AS c WHERE c.userid = 1),
banks = (SELECT RAW b FROM default ub UNNEST ub.bank AS b WHERE b.userid = 1);