I have a factory for an interface with different implementations. But one implementation needs an extra method which the others don't need. How do I solve this without implementing "not implemented exception" methods in other implementations?
Do the consumers of the inteface need to call the method that is only required for one implementation?
If the consumer does not need to call the method, it is an implementation detail. Therefore, it is not of interest to the consumers of the interface, as they even should/must not call it. Just add the method as a private method of the implementation that needs it.
If on the other hand the method must be accessible for the consumers of the interface, you are violating the Interface segregation and Liskov substitution principles. Extract the method in an own interface.
Do not add the method to the interface. If the method is relevant only for that one implementation, only add it to that one. The point of the interface is to abstract the common elements of every factory, so a method specific to a single factory should not be in the general factory interface.