StackOverflow question https://stackoverflow.com/questions/64650162/javafx-combobox-remove-selected-item

Test.java

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

/**
 * JavaFX App
 */
public class App extends Application
{

    @Override
    public void start(Stage primaryStage)
    {
        ComboBox<String> comboBox = new ComboBox();

        comboBox.getItems().add("Choice 1");
        comboBox.getItems().add("Choice 2");
        comboBox.getItems().add("Choice 3");

        //Remove old on new selection.
        comboBox.getSelectionModel().selectedItemProperty().addListener((ov, t, t1) -> {
            if (t != null) {
                comboBox.getItems().remove(t);
            }
        });

        //Remove selected item on button press.
        Button btn = new Button("remove");
        btn.setOnAction(t -> {
            String selectedItem = comboBox.getSelectionModel().getSelectedItem();
            comboBox.setValue(null);
            comboBox.getItems().remove(selectedItem);
        });
        VBox vBox = new VBox(comboBox, btn);

        Scene scene = new Scene(vBox);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args)
    {
        launch();
    }
}