Unable to play downloaded movies from iPhone

Using HEIF or HEVC media on Apple devices - Apple Support

1. If the iPhone recorded in H.265 HEVC, then you can configure to download as H.264 AVC, if your workflow likes that better.
2. If H.265 is unsupported, then you can configure iPhone to record in H.264 next time.

QuickTime Player for Windows is very old and now unsupported. Please use different playback software. It is not needed to play .mov files.

The download might not have completed properly, causing the file to become corrupted. Try downloading the movie again and ensure the download is fully complete.