If the “Select File” button is not visible in full-screen mode, it may be caused by a display issue, browser zoom settings, or an unsupported website layout. Try refreshing the page, reducing the browser zoom to 80–90%, or exiting full-screen mode to see whether the button reappears.. You can also try opening the page in another browser or clearing the browser cache. If the problem continues, check whether the website requires specific permissions to access files on your device. Ensure you select files only from trusted websites and never upload sensitive documents unless necessary.