Problem with ObjectId as primary key

can’t write user custom data from client
could do so when my “User” data model had primary key as a UUID string
now I have ObjectId and following the example in documentation

 func insertOne() {
        let user = app.currentUser!
        let client = user.mongoClient("mongodb-atlas")
         let database = client.database(named: "")
         let collection = database.collection(withName: "User")
         // Insert the custom user data object
            "_id": AnyBSON.objectId(ObjectId)

throws an error

Cannot convert value of type 'ObjectId.Type' to expected argument type 'ObjectId'


"_id": AnyBSON(

used to work fine when _id was uuid string
no wonder…
Andrew Morgan uses it in his Chat App !!!
but why???