Because Microsoft never released an official "AIO" ISO, any file found online with this description is .

If you have a valid product key and specifically need 8.1 for older hardware, you should only download it from the official source to ensure the file is clean: Microsoft Windows 8.1 ISO Download Page. Steps: Select the edition (Windows 8.1). Select your product language. Choose the 64-bit or 32-bit download. Burn the ISO to a USB drive using a tool like Rufus . Recommended Alternatives

Modified ISOs may have essential system components removed to save space, leading to frequent crashes. Official Way to Get Windows 8.1 (Legacy)