Stackoverflow question: https://stackoverflow.com/questions/74421996/javafx-multiple-choice

App,java

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.ColumnConstraints;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.RowConstraints;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;


public class App extends Application {

    
    
    @Override
    public void start(Stage primaryStage) {
        LocalDate localDate = LocalDate.now();
        
        GridPane gpRoot = new GridPane();
        gpRoot.setHgap(3);
        gpRoot.setVgap(3);
        
        
        
        List<User> users = new ArrayList();
        users.add(new User("John Doe"));
        users.add(new User("Kim Doe"));
        users.add(new User("Jane Doe"));
        
        
       
        generateHeader(localDate, gpRoot);
        
        for(int i = 0; i < users.size(); i++)
        {
            generateRow(localDate, users.get(i), gpRoot, i + 1);
        }
        
        
        StackPane root = new StackPane(gpRoot);
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
    
    public void generateRow(LocalDate localDate, User user, GridPane gpRoot, int row)
    {        
        Label lblName = new Label(user.getUserName());        
        lblName.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
        lblName.setAlignment(Pos.CENTER);
        gpRoot.add(lblName, 0, row);
        
        for(int i = 0; i < localDate.lengthOfMonth(); i++)
        {
            int day = i + 1;
            
            StackPane stackPane = new StackPane();
            stackPane.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
            stackPane.setOnMouseClicked((t) -> {
                if(stackPane.getStyle().isEmpty())
                {
                    stackPane.setStyle("-fx-background-color: lightblue;");
                    LocalDate selectedDate = LocalDate.of(localDate.getYear(), localDate.getMonth(), day);
                    user.getSelectedDates().add(selectedDate);
                    
                    System.out.print(user.getUserName() + ": \t");
                    user.getSelectedDates().forEach(date -> System.out.print(date + "\t"));
                    System.out.println();
                }
                else
                {
                    stackPane.setStyle("");
                    LocalDate selectedDate = LocalDate.of(localDate.getYear(), localDate.getMonth(), day);
                    user.getSelectedDates().remove(selectedDate);
                    
                    System.out.print(user.getUserName() + ": \t");
                    user.getSelectedDates().forEach(date -> System.out.print(date + "\t"));
                    System.out.println();
                }
            });
            
        
            gpRoot.add(stackPane, day, row);
        }
    }
    
    public void generateHeader(LocalDate localDate, GridPane gpRoot)
    {        
        gpRoot.getColumnConstraints().add(new ColumnConstraints(100));
        gpRoot.getRowConstraints().add(new RowConstraints(25));
        
        Label lblDate = new Label("Date: ");
        lblDate.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
        lblDate.setAlignment(Pos.CENTER);
        gpRoot.add(lblDate, 0, 0);
        
        for(int i = 0; i < localDate.lengthOfMonth(); i++)
        {
            gpRoot.getColumnConstraints().add(new ColumnConstraints(25));
            Label lblNumberDate = new Label(Integer.toString(i + 1));
            lblNumberDate.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
            lblNumberDate.setAlignment(Pos.CENTER);
            lblNumberDate.setStyle("-fx-background-color: yellow;");
            gpRoot.add(lblNumberDate, i + 1, 0);
        }
    }
}

User

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

/**
 *
 * @author Sed
 */
public class User {
    private String name;
    private List<LocalDate> selectedDates = new ArrayList();

    public User(String name) {
        this.name = name;
    }

    public String getUserName() {
        return name;
    }

    public void setUserName(String name) {
        this.name = name;
    }

    public List<LocalDate> getSelectedDates() {
        return selectedDates;
    }

    public void setSelectedDates(List<LocalDate> selectedDates) {
        this.selectedDates = selectedDates;
    }
    
    public void addSelecterdDate(LocalDate localDate)
    {
        this.selectedDates.add(localDate);
    }
}