My laptop keyboard is not working right now, and I use my backup external keyboard that doesn’t have Fn Key. I use several alternative shortcuts. You can customize all the Keys based on your preference.
Prerequisite
amixer from alsa-utils
brightnessctl
Volume Up
Key: Ctrl + Up (keypad)
Command: amixer -q -D pulse sset Master 5%+
Volume Down
Key: Ctrl + Down (keypad)
Command: amixer -q -D pulse sset Master 5%-
Brightness Down
Key: Ctrl + Left (keypad)
Command: brightnessctl set +5%
Brightness Up
Key: Ctrl + Right (keypad)
Command: brightnessctl set 5%-
These shortcuts were tested on LinuxMint Xfce. I will update this article when I make a new shortcut. I hope this is useful for you.
Thank you.
