Strange iPhone screen lights up and stays on at night.

I have an XS Max with iOS 17.4.1. After an update back in March or late February, the screen comes on at night. This is not just a notification turning it on and then it goes off again. I've never seen this screen at any other time, but it looks like some sort of lock screen. It comes on with the full brightness of the display and stays on indefinitely until I pick up the iPhone or hit a button. When I pick it up, the screen slowly dims to the normal settings, and the normal lock screen slowly fades in from black. It only happens at night, but not every night - maybe once a week. I've fiddled with focus settings, but only after this started happening. They did not help. These white lights are too saturated to make out in the photo, but across the top are my wireless carrier, a lock icon, and the three small icons for Cell, WiFi and Battery. The bottom row is Flashlight icon, a long slide-up bar and the camera icon. Any clues are really appreciated.