Another update: I just tried 550.54.14 on kernel 6.6.35, with the same nvidia.NVreg_RegistryDwords=EnableBrightnessControl=1 acpi_backlight=native present in my GRUB_CMDLINE_LINUX_DEFAULT. Backlight control still doesn’t work. The observable behavior is identical to [NVIDIA Beta driver 545.23.06] Brightness not working / changing - #13 by ddadap.