lightdm - How to enable numlock at boot time for login screen in Ubuntu 18.04?

I have a fresh 18.04 install and would like to enable the numlock key for login, without switching to the older lightDM. I saw this, this and this, but when trying the gdm approach I get: Command 'gdm' not found
but as said above I would like to achieve this small task, without having to switch to lightDM or do some other major changes.

Do the following:

xhost +SI:localuser:gdm

sudo su gdm -s /bin/bash

Now, you need to use gsettings or dconf #or dconf-edit if you have it

Go to /org/gnome/settings-daemon/peripherals/keyboard/numlock-state and change it to on

or simply after the two lines do this

dconf write /org/gnome/settings-daemon/peripherals/keyboard/numlock-state "'on'"

or

gsettings set org.gnome.settings-daemon.peripherals.keyboard numlock-state 'on'

Now reboot