Trying to get my brightness working

My brightness control suddenly stopped working, when it did. I didn’t do much changes to my system, so I suspect there’s a recent kernel change, or anything else of a similar kind (e.g. a systemd update) that broke it. However I’ll try to journal that here.

My issue is basically the same as in the thread [SOLVED] /sys/class/backlight empty, but I have a laptop screen indeed, not an external display. And, again, everything worked just days ago.

What I’ve tried? Things written in that forum post: I tried all possible backlights kernel parameters:

acpi_backlight=video and none and native and vendor.

Note: there should be just one string of these 4 variants, not all at the same time. It was unclear to me from the ArchWiki’s interface, but Gentoo wiki helped me here.

I did sudo mkinitcpio -p linux as well.

My config is: MacBookPro 8,1 (Sandy Bridge) with Intel GPU (6th gen).

More details:

OS: Arch Linux x86_64 
Host: MacBookPro8,1 1.0 
Kernel: 6.1.5-arch2-1 
WM: sway 
Terminal: foot 
CPU: Intel i5-2415M (4) @ 2.900GHz 
GPU: Intel 2nd Generation Core Processor Family 
Memory: 1689MiB / 15913MiB