What is protected virtual new

protected means that it is visible only inside this class and classes derived from it.

virtual means that it can be overriden in derived classes.

new means that here you create new overriding hierarchy, i.e. you stop overriding the method defined in the base class and replace it with this method.

More details can be found here

new is used for member hiding.

Unlike an overridden method, a new method will not be called by a reference to the base class.

See the documentation.