White exclamation with yellow lightning screen flashed on my iPhone 12

I was playing a game when my iphone 12 screen went dark for a second then flashed a horizontal band with a black background and in the middle was a white exclamation mark under white bars slanted together to touch at the top. On either end of the band were lightening streaks glowing yellow.

it flashed like a warning then went dark… a few seconds later it flashed again, then went dark. I froze and waited for it to happen again but my phone went off. I dared to touch the screen and nothing happened. I pressed the power button to start my phone and nothing happened. Then a few seconds later my Home Screen showed up.

I’ve never seen it before and haven’t found a similar screenshot online. Is it a hack? A virus? I don’t think it’s part of the game i was playing … Picture Cross. I don’t know how but my phone took a video of it and i was able to get this screenshot

[Re-Titled by Moderator]

update: It is part of Picture Cross. I went back in and I got the same thing after playing a while. Not sure why though.