Let's try manually whether backlight interfaces work.
cd /sys/class/backlight/radeon_bl0 # get max brightness cat max_brightness # get current brightness cat brightness # change current brightness, assuming max=120000 echo 120000 | sudo tee brightness echo 60000 | sudo tee brightness
Once done, did you see brightness changed?
Let's try manually whether backlight interfaces work.
cd /sys/class/ backlight/ radeon_ bl0
# get max brightness
cat max_brightness
# get current brightness
cat brightness
# change current brightness, assuming max=120000
echo 120000 | sudo tee brightness
echo 60000 | sudo tee brightness
Once done, did you see brightness changed?