Hi petitminion,
I don’t think I can help much, but reading through the thread you linked and also a somewhat older one Laptop backlight control regression with 465.24.02 this can be related to a number of other reasons as well.
One for example that the integrated graphics on the CPU controls backlight settings instead or similar.
The bug listed in the other thread is marked fixed, but then again it was rather Lenovo specific, so it might be Acer handles backlight control differently.