It’s a screen time indicator that takes the form of a colored vertical bar which represents the 24-hour night/day cycle. Thus, you just get an “insight”, a preview, of your phone usage. Every time the phone is unlocked, it leaves a groove and vice versa. Through the insight of those grooves, take a peek at your digital life. It encourages users to spend more time enjoying life and less time unlocking their smartphones.
Path: Settings > Wallpapers & style > Always-On Display > Personalized > System-provided > Insight.
Note: Only OLED screens support this feature, but not all OLED screen models support the feature.