Users should be cautious of double-extended files from unknown sources, as they can sometimes be used to hide malicious scripts through steganography. How to Handle the File

The ".mp4.mp4" suffix typically occurs when a user manually renames a file or when a conversion tool adds a second extension to a file that already had one.

If you have this file and are unable to open it, follow these steps: A Quick Dive Into MP4 - DEV Community

Apps like Telegram or WhatsApp often assign long numerical strings to cached video files.

As a container, this file can store video tracks, audio, subtitles, and metadata in separate "atoms" or boxes.