Database
[{"_id":1,"first_name":"Tom","email":"tom@example.com","ACL":{123gd:{read:true,write:false,},3sg2w:{read:true,write:false,}}},{"_id":2,"first_name":"Tom","email":"tom@example.com","ACL":{546er:{read:true,write:false,},98trw:{read:true,write:false,}}}]
Query
db.collection.find({$expr:{"$anyElementTrue":{"$map":{"input":{"$objectToArray":"$ACL"},"as":"kv","in":{$eq:["$$kv.k","123gd"]}}}}})