Wrapps scruss's shutdown script in an installer because i'm lazy :)
When a momentary switch is attached to GPIO pin 21 and shorted to ground the following behaviour is observed
< 2 seconds == nothing
> 2 && < 5 seconds == reboot
> 5 seconds == shutdown
wget https://raw.githubusercontent.com/maz0r/rpi-shutdown/main/rpi-shutdown.sh
sudo chmod x rpi-shutdown.sh
sudo ./rpi-shutdown.sh