Services like iCloud or Dropbox often use this naming convention when you "Export" or download files to a desktop.
Since it is a QuickTime movie, it is compatible with most modern media players: 2021-10-21 16.45.43.mov
Most likely recorded on an iPhone or iPad . When you transfer a video from an iOS device to a computer via a direct cable or certain cloud services, the device often renames the file from a generic label (like IMG_1234 ) to this precise timestamp. Services like iCloud or Dropbox often use this