Just an idea for Tasker nerds amongst you. Maybe it can help you debugging the brightness issue? There is a command called "Custom setting" which can get/set values from Android settings. Screenshot is related. Not having a Samsung phone myself.
Do you mean the view on my screenshot ?
The Tasker options look a bit different for me.
The display still gets darker
P.S.:
I wrote a short task. The display brightness is permanently set to maximum brightness after 20 seconds.
No success. The problem is that the display dims but the settings remain at maximum brightness.
When I manually dim the display, the display always brightens after 20 seconds.
The task works.
The display gets darker without changing the slider.