In display configuration settings marked with “Brightness” there is a checkbox “Control hardware brightness with DDC/CI” and underneath it is a slider. The slider controls brightness with software and checking the hardware brightness checkbox changes the behaviour of that slider. When I recently started using linux this confused me, I assumed that I must click this checkbox in order for it to have any effect on the brightness at all. Hardware brightness has way more limited range of control than software brightness. This UI confusion is an accessibility issue to me as me and many others autistic people are prone to painful overstimulation which was happening due to brightness controls being hardware limited.
This settings menu can be improved by adding another slider to allow simultaneous software and hardware brightness control or if it isn’t possible instead of a checkbox making it a toggle (between software and hardware control).