If you must use a third-party ISO for research or legacy testing:
When searching for a "Windows 8 All-in-One ISO Pre-activated" file, it is important to understand that such files are almost exclusively of the original operating system.
These files often contain hidden keyloggers, miners, or backdoors that allow hackers to access your personal data or remote-control your PC.
Many older Windows 8 machines can run Windows 10. You can download the official Media Creation Tool directly from Microsoft.