Try this code:
import org.openqa.selenium.WebDriver
import org.openqa.selenium.chrome.ChromeDriver
import com.kms.katalon.core.webui.driver.DriverFactory
import com.kms.katalon.core.webui.keyword.WebUiBuiltInKeywords as WebUI
System.setProperty("webdriver.chrome.driver",
DriverFactory.getChromeDriverPath())
WebDriver driver1 = new ChromeDriver()
WebDriver driver2 = new ChromeDriver()
// first browser
DriverFactory.changeWebDriver(driver1)
WebUI.navigateToUrl("https://www.duckduckgo.com")
// second browser
DriverFactory.changeWebDriver(driver2)
WebUI.navigateToUrl("https://www.google.com")
// first browser
DriverFactory.changeWebDriver(driver1)
WebUI.maximizeWindow()
// second browser, navigate from duckduckgo to Katalon
DriverFactory.changeWebDriver(driver2)
WebUI.navigateToUrl("https://katalon.com")
Tested in Katalon Studio 7.9.0rc
