There are a number of factors. In my case it's the driver of the graphic card.
I never had problems with sleep on any of my Linux laptops. The problem is with shutdown. Shutdown is shutdown when I'm using the Noveau driver for my NVidia card but it's reboot when I'm using the NVidia driver. Unfortunately Noveau doesn't get sync right for my card with both Wayland and X11 so I have to use NVidia with X11. The few times per year that I have to poweroff I press the power button right before the BIOS screen appears.
At least version 470 of the driver fixed the brightness control keys. The didn't work for years and I remapped them as hotkeys to run xbacklight.
