You cannot set additional properties on the Sign Up screen.
The user first needs to sign up that a records is created in the user collection.
Now you can update the additional properties.
Best way to do this is on a separate screen after sign up, where the user e.g. maintains the profile picture etc. You can set the properties here in automatic fields.
It usually does not work to add a second action on the sign up screen itself, because of timing problems with the network/database. (You would try to update a record which could be still in process)