Why is MongoDB timestamp is disabled?
That's because you really don't want to use timestamp which is a MongoDB-internal data type: https://docs.mongodb.com/manual/reference/bson-types/#timestamps
You want to use date which is really an ISODate data type https://docs.mongodb.com/manual/reference/method/Date/ or alternatively use string with a format date-time, ideally formatted according to ISO 8601.
Alternatively, you may want to use a String data type with a date-time format.
We do display the timestamp data type for backward compatibility purposes, but disabled it so users would not be tempted to use it.