I also have the same problem on my Asus Tuf Gaming A15 (2022) laptop. If I use any kernel above 5.15 (LTS), including 5.16, 5.17 etc and all kernels starting with 6, the screen brightness/backlight is locked to max. It’s just too bright. I tried switching between x11 and wayland on the login screen but it didn’t change anything. I don’t know what they’ve changed after the kernel 5.15 but it removed my laptop’s capability to reduce backlight. The brightness slider can be seen on the screen when I press Fn+F7 or F8 but it doesn’t change anything.
I’m using KDE Plasma. Everything is up to date. I’m using the open source drivers for the nvidia gpu but I mostly use the integrated amd gpu anyway. If there’s any info I need to provide, please tell me what it is and how to get it. I’m not very familiar with terminal commands.