I can certainly disable the screen altogether, regardless of desktop environment, but that’s not the same thing as turning the backlight to zero.
Admittedly I am on x11 and not wayland, not sure if there’s a workaround in wayland that works better (perhaps Plasma is doing some magic there?).
In either case, relying on dpms and temperature shifting to approximate functionality is still just workarounds for what appears to be a bug/limitation of the AMD frameworks’ firmware (a limitation that is not present on the intel version, or any other laptop I’ve used). 
Perhaps it’s worth opening a fresh thread?
P.S. Hey fellow Python http alum!