sudo nano /etc/gdm3/greeter.dconf-defaults
set sleep-inactive-ac-timeout
to 0
Note: You might need to restart your computer (or find a way to reload gdm3)
sudo nano /etc/systemd/logind.conf
set HandleLidSwitchExternalPower
to ignore
After changing the setting, run:
systemctl restart systemd-logind.service
sudo nano gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 0
sudo nano gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type nothing
WARNING: This means you won't be able to perform sleep or hibernation at all!
sudo systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target