How MP4 organizes metadata
An MP4 is a tree of boxes (atoms). Video and audio live in mdat; everything that describes the file lives in moov. That's where Android phones write GPS (©xyz), where editors write their own name (©too) and where the file records when it was created (creation_time in mvhd and in each track).
Adobe apps add an XMP block with CreatorTool, DocumentID and sometimes save history. Exports from editing apps usually keep the encoder name, which reveals the producer's workflow.
Why clean an MP4 before sending it
Platforms like Instagram and TikTok re-compress files and drop most of these atoms. Email, Google Drive, WeTransfer, WhatsApp documents and client deliveries keep the original MP4, with location, dates and project names.
Why converters and commands aren't enough
Converting the MP4 in another app usually re-encodes the video and often copies the same atoms into the new file. Command-line tools remove global metadata but keep track names and encoder markers inside the stream. MetaRemove also cleans that residue, without re-encoding, and shows before and after.