What your iPhone writes into every video
The MOV (QuickTime) format stores metadata as key–value pairs in the meta box. The iPhone fills the com.apple.quicktime.* keys: ISO 6709 location with altitude, horizontal GPS accuracy, make, model, iOS version and a date with time zone.
Videos that belong to a Live Photo also carry a content.identifier that links the video to its photo. None of it shows while watching.
Turning off location when sharing isn't enough
When sharing from Photos, you can turn off location under Options. The file you send still carries model, iOS version and date, and the option applies only to that share; the original in your library keeps everything.
Does converting to MP4 remove the metadata?
Not always. Many converters copy the QuickTime keys into the MP4, and they re-encode the video, losing quality. MetaRemove cleans the MOV itself, with no conversion and no re-encoding.