Screen randomly sims and YES all auto brightness settings are off

iPhone XR has issue where my screen with randomly dim. Before people ask I have tried it all. 1- the screen dimming slider from dock is always full. 2- Settings/Display and Brightness the brightness gauge is full, and True Tone is off. 3- Settings/General/Accessibility/Display accommodations is off and all settings there are off.

Note: this also happened on my pervious phone (8 Plus).

help or suggestions please