iPhone12 sends blank videos

iPhone12 mini sends blank videos: a video I can see perfectly fine on my phone shows up as a blue-green audio only attachment when I attempt to mail it from the photos app.

I have read that this is because the recipient device with older software can't read the encoding on the new phone video.

But this is happening if I send the video to myself, to view again on the iPhone12 mini. It cannot 'see' its own video.

It seems like a deeper problem with iOS14 not being able to correctly add the image to the mail message.