After having installed Linux Mint 19.3 on an old MacBook Pro I wanted to be able to use the function keys without having to press on the ‘Fn’ key
Here is the answer:
You can run a simple command to change the behavior.
echo 0 > /sys/module/hid_apple/parameters/fnmode 0 = Fn key disabled 1 = Fn key pressed by default 2 = Fn key released by default
Therefore to get what I wanted the command is:
echo 2 > /sys/module/hid_apple/parameters/fnmode
To make it survive a reboot you just need to add the following to
echo "options hid_apple fnmode=2" >> /etc/modprobe.d/hid_apple.conf