MongoDB unique field

Hey there,
Is there a way to make a mongoDB field “unique” through parse dashboard or server? Like objectId is by default.

If you are there, yes.
You can create a unique index on the dashboard

This is not a feature of the open source version of Parse Dashboard. You would need to create an index directly in the MongoDB cluster. If you are using a hosted Parse Server provider, then it depends on their dashboard and I suggest to consult their documentation or open a support ticket with them.