I was at my son’s sunny soccer game yesterday and, when I looked down at my Apple Watch Series 5 I could barely see the display as the sun was hitting it directly. I noticed this flashing. The video looks like a band across the screen, but in real life the entire screen was flashing. It looks to be roughly once a second so I think what we’re seeing is the variable refresh rate of the LTPO display in “off” mode. Pretty cool!