Backlight brightness very low when using nvidia-driver-510 or newer. (Ubuntu 22.04)

I have a Razer Blade Pro 17 (2017) with 4K IGZO G-Sync Sharp CRX1200 display and GTX 1080 GPU. (RZ09-01663) On Ubuntu 22.04, using nvidia-driver-470, the backlight brightness is stuck at full. (I don't really mind that.) However, if I upgrade to any of the newer drivers (510, 515, 520) the brightness control works, but maximum brightness is very low, maybe 20% of what I see on the 470 driver. I can barely read any text. I now need features from the 520 driver for my work, so I have no choice but to upgrade. As a workaround, I'm using an external HDMI monitor, but it's frustrating that the laptop's own display is now basically useless. I tried using various backlight brightness utilities and config file hacks, but so far nothing works. I can adjust brightness by poking values into "/sys/class/backlight/nvidia_0/brightness", But even at max settings (100) the screen is very dim. "xrandr --output DP-0 --brightness 1.5" helps a little, but that only adjusts color profile, not the backlight. Is there some way to make the backlight as bright as it was with the 470 driver?