Try covering (black electrical tape) the infrared led next to the selfie camera. You can shine a bright light to find it, it will sparkle red. I have a suspicion some Android versions are constantly activated the led.
The downside is the screen won't turn off when you put the phone to your ear, and also you won't be able to use face unlock.
Covering the IR make my Unihertz Jellystar perfect for my eyes. Although additionally I have to run it on full brightness due to PWM (Lucky the screen is not too bright)