Selenium click() doesn't work on new opened window

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Java

JavaSE

Java8

after logging in, the webiste opens in a new window which has the same url with the time before logging in to the website. but after that, mo click on no element works:

System.setProperty("webdriver.firefox.marionette", "some directory"); 
    		  
    		   WebDriver driver = new FirefoxDriver();
    		     
    		   driver.get("https://www.playok.com/en/spades/");
          
    		   
    		   driver.findElement(By.cssSelector("button.ckbut.but0")).click();
    		   

    		   driver.findElement(By.cssSelector("button.lbpbg.ttup")).click();
    		   WebElement username = driver.findElement(By.cssSelector("input#id"));
    		   username.sendKeys("some username");
    		   WebElement password = driver.findElement(By.name("pw"));
    		   password.sendKeys("some password");
    		   driver.findElement(By.cssSelector("input.bxpad.ttup")).click();//here a new page opens at the same window, which has a start button:
    		   
    		   driver.findElement(By.cssSelector("button.lbprm.ttup")).click();//here a new window opens which goes to the main game page and the url is still the same
    		   
    		  //but the following click doesnt work; actually no button works, doesnt matter if here a sleep() gets used, click won't work anyway.
    		   driver.findElement(By.cssSelector("button.butsys.minwd")).click();

What I have tried:

almost all the buttons were tested; also a sleep() has been used there, but no difference; still no button works.

but there is no other way to access to the website without logging in, and when logging in, this problem accurs.