无法在 java selenium 中找到元素

问：

大家好，我无法在最后一行代码上与“索引”交互，代码对所有项目都正常工作，除了嵌套框架，它给出错误，因为无法找到元素，我已经尝试了 xpath 和链接文本，但仍然收到此错误，这是一个用于测试自动化实践的演示网站，错误仅适用于代码最后一行的索引代码的其他部分工作正常。

package sdet;
import org.openqa.selenium.*;
import org.openqa.selenium.By;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.interactions.Actions;
import org.openqa.selenium.support.ui.ExpectedConditions;
import org.openqa.selenium.support.ui.WebDriverWait;
import org.openqa.selenium.WebElement;

import java.awt.event.ActionEvent;
import java.time.Duration;
import java.util.*;

public class selenium {

    public static void main(String[] args) throws InterruptedException {
        // TODO Auto-generated method stub
System.setProperty("Pathtochromedriver");
WebDriver driver = new ChromeDriver();
driver.get("https://testpages.herokuapp.com/");
driver.manage().window().maximize();
// Clicking on basic webpages //
driver.findElement(By.id("basicpagetest")).click();
String  Urlnow = driver.getCurrentUrl();
System.out.println("current url is :" +Urlnow );
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("elementattributestest")).click();
Thread.sleep(2000);
driver.navigate().forward();
JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("javascript:window.scrollBy(250,350)");
Thread.sleep(2000);
WebElement Addattribute = driver.findElement(By.xpath("//button[@class=\"styled-click-button\"]"));
Actions actions = new Actions(driver);
actions.moveToElement(Addattribute).doubleClick().build().perform();
Thread.sleep(2000);
driver.navigate().forward();
js.executeScript("window.scrollBy(0,-400)");
// Clicking on index here // 
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("findbytest")).click();
Thread.sleep(2000);
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("tablestest")).click();
Thread.sleep(2000);
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("dynamictablestest")).click();
Thread.sleep(2000);
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("alerttest")).click();
driver.findElement(By.id("alertexamples")).click();
driver.switchTo().alert().accept();
// Clicking on show confirm box //
driver.findElement(By.id("confirmexample")).click();
Thread.sleep(2000);
driver.switchTo().alert().dismiss();
Thread.sleep(2000);
driver.findElement(By.linkText("Index")).click();
driver.findElement(By.id("fakealerttest")).click();
// Clicking on showalertbox //
driver.findElement(By.id("fakealert")).click();
driver.findElement(By.id("dialog-ok")).click();
// Clicking on modal dialog //
driver.findElement(By.id("modaldialog")).click();
driver.findElement(By.id("dialog-ok")).click();
Thread.sleep(2000);
driver.findElement(By.linkText("Index")).click();
// Clicking on frames test //
driver.findElement(By.id("framestest")).click();
Thread.sleep(4000);
driver.navigate().forward();
driver.findElement(By.linkText("Index")).click();

//driver.findElement(By.id("framestest")).click();
//Thread.sleep(2000);
//driver.findElement(By.linkText("Index")).click();


}

}