Selenium isn’t able to detect or interact with system-level popups like the "Save As" dialog because it only operates within the browser’s DOM. These popups are actually controlled by the operating system, not the browser, which puts them outside Selenium’s reach. To work around this, people often turn to external tools like AutoIt, WinAppDriver, or PyAutoGUI. A better solution, tho, is to configure the browser to automatically download files by adjusting its settings to skip the prompt altogether. Another reliable and often more efficient option is to download the file directly using its URL with HttpClient in C#.