Recently I accidentally uninstalled some packages on my machine which damaged the gnome-control-center and the NetworkManager/netplan on my Ubunut 20.04.
The solution was quite simply:

sudo apt-get install --reinstall gnome-control-center

But without a configured network interface it was impossible to do this offline…
But with

sudo dhclient <interface>

It was possible to get a configuration (IP address, gateway, …) and than the fix was quite straight forward.