If you have deactivated the automatic brightness control of the display on the Huawei P20 Pro, you may notice that the screen brightness is still controlled. This can be due to a special setting that has been activated in the developer options.
To find this option on the Huawei P20 Pro and to check if it is enabled, navigate to the following submenu: Open the developer options.
These are located under: Settings -->System --> Developer Options
Then scroll down the list until you see the following entry: Sunlight readability If active, deselect this option.
The Huawei P20 Pro should no longer automatically adjust the display brightness when the light conditions around you change.