Comment # 13 on bug 1217750 from varval761

No worries!

I actually was just now able to try the proprietary Nvidia driver. It actually
has the same issue as nouveau, with the brightness keys not working and trying
to set it in "/sys/class/backlight/nvidia_wmi_ec_backlight" gives the same
invalid argument error. In fact, max_brightness is 0 and brightness is stuck at
145. I even tested it on different OS's (Pop!_OS and Nobara, which have
pre-installed Nvidia ISO's) and same issue with both.

Unless I'm missing extra steps to try after installing Nvidia driver?