Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Can’t replicate the issue with my iPhone 12 either.

Attempted the video playback at various brightness(10%, 30%, 60% and 90%) in a dark room, it just looks like the phone is off.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.