@Test
    public void foo() throws MalformedURLException {
        // You have to setup some Selenium grid to use RemoteWebDriver
        ChromeOptions chromeOptions = new ChromeOptions();
        RemoteWebDriver driver = null;
        try {
            driver = new RemoteWebDriver(new URL("http://localhost:4444/wd/hub"), chromeOptions);
            driver.get("https://www.w3schools.com/html/html_iframe.asp");
            driver.switchTo().frame(0);
            driver.switchTo().defaultContent();
        } catch (Throwable e) {
            throw e;
        } finally {
            if (driver != null) {
                driver.quit();
            }
        }
    }

System info: host: 'bo-MS-7B86', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'amd64', os.version: '5.11.0-40-generic', java.version: '1.8.0_302'
Driver info: org.openqa.selenium.remote.RemoteWebDriver
Command: [6adcb1735cb29eb0dccefcc24f1dd320, switchToFrame {id=null}]
Capabilities {acceptInsecureCerts: false, browserName: chrome, browserVersion: 96.0.4664.45, chrome: ..., javascriptEnabled: true, networkConnectionEnabled: false, pageLoadStrategy: normal, platform: LINUX, platformName: LINUX, proxy: Proxy(), setWindowRect: true, strictFileInteractability: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: dismiss and notify, webauthn:extension:credBlob: true, webauthn:extension:largeBlob: true, webauthn:virtualAuthenticators: true}
Session ID: 6adcb1735cb29eb0dccefcc24f1dd320
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:583)
	at org.openqa.selenium.remote.RemoteWebDriver$RemoteTargetLocator.defaultContent(RemoteWebDriver.java:1042)
	at com.example.demo_selenied.MainPageTest.iframeTest2(MainPageTest.java:106)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    ...
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException
	at org.openqa.selenium.remote.TracedCommandExecutor.execute(TracedCommandExecutor.java:47)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:559)
	...