I'd like to find a way to control the display backlight brightness using the method in use before Mojave. The method I'm looking for may be even older.
I have one of the cursed late-2011 Macbook Pros with the failed AMD Radeon graphics. Using the excellent solution from dosdude, I have disabled the AMD discrete graphics and everything runs fine using the Intel graphics. Everything EXCEPT adjusting screen brightness. (I think there are other issues with sleep but that doesn't concern me.) Symptoms include no response to the F1 and F2 buttons and no slider in System Preferences. Most folks get max brightness all the time. I was living with that until a recent update to 10.14.6. Now I'm locked at some lower level.
Loss of brightness control is a well-documented shortcoming of the dosdude fix. It's a small price to pay to unbrick your Macbook! But it would be awesome to restore dimming.
Anyway, the loss of brightness control corresponds to a system upgrade. I think dimming worked fine under Sierra but disappeared with High Sierra. Possibly it was Mojave that killed it. I'm sure the details are in the dosdude patch thread and I could retrieve those details if it matters. The possibility of returning to the dimming control used back then is tantalizing. Maybe that's because I have no idea how impossible it is?
If there was an easy approach to this I'm pretty sure a talented guy like dosdude would have found it. So I'm wondering if he left some stone unturned. Some kext replacement or such that might restore dimming to all of us suffering along with one of Apple's rare lemon models.