Just a quick note to my self
We mostly want to run LTS-versions only, of Ubuntu.
In case you absolutely need to update, in between LTS-versions, this is how it’s done:
Ubuntu 18.04 upgrade to Ubuntu 19.04 (not LTS)
nano /etc/update-manager/release-upgrades
-> Prompt=normal
sudo apt update && sudo apt dist-upgrade -y
sudo do-release-upgrade