[{"_id":{"$oid":"62dfef1a6fa3ca52622b02e4"},"dealer_id":1499,"credentials":{"62e12c210b2d6":{"account_id":"942646","terminal_id":"310012","provider":"Epay","supplier":"verizon","username":"hello","password":"world","portal_link":"https://localhost","certificate_key":"olsjhflsaknfdlaksfd","certificate_file":"aa.txt"}},"updated_at":{"$date":{"$numberLong":"1659553693372"}},"created_at":{"$date":{"$numberLong":"1658842906093"}}}]

db.collection.find({$expr:{$gt:[{$size:{$filter:{input:{$objectToArray:"$credentials"},cond:{$in:["hello",{$map:{input:{$objectToArray:"$$this"},in:"$$this.v.username"}},]}}}},0]}})