Apologies, I overlooked what you might set there. Instead of 'manual' set 'Automatic (DHCP) addresses only' and then you will not need to fill in any ip settings, and only the DNS servers section will need to be filled in with the 8.8.8.8.
Hopefully the command:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 379CE192D401AB6
Will work after that.
I believe you already ran
echo "deb https://deb.etcher.io stable etcher" | sudo tee /etc/apt/sources.list.d/balena-etcher.list
so you dont need to run that again.
Send me a screenshot of your network settings page after changin the above so I can check you did it correctly.
P