Why does the screen flicker when the light intensity of external light sources changes drastically?

Your phone screen supports highlight mode under strong light. This is a common characteristic of all OLED screens. When the sensor detects that the intensity of ambient light reaches a certain level, it automatically enters highlight mode for better visibility. The moment you enter or exit highlight mode, the brightness changes, making you feel that the screen is flickering. This is normal and does not indicate an issue with your phone. If you are not satisfied with the brightness of your screen, you can disable automatic brightness adjustment feature by going to Settings > Show > Brightness.